And I'm kind of tired to do this. I want to rest...

My summary:
1. IEM = headphones on HATS and can compensated by OW.
2. Measurement data is different with what you really hear.

sarcasm.. I wish you can understand my situation.
Best way I can do now is follow the Internationally Verified Ways. Because this data is not just for me.

Thanks.

Probably because nobody bothered to create a reasonable compensation (IMO).
To do this you would have to have a 'standard insertion depth', tube diameter and length and calculate what the frequency response of that small piece of pipe (which is sealed on both ends).

There is too many variables to match it to how it sounds (as Speakerphone also pointed out) because of all the things involved.

As there are already standards it feels logical to follow them.
However, if the couplers are are closely the same it makes sense to publish the raw plots as these can easily be compared.
They can also be compared using 'standard' compensations but one should pick just one.

On the other hand I am a strong proponent of creating a 'standard' using a transparant 'tube' with depth markings so all inserted IEM's actually measure and can be compensated the same way.
Then the next step would be to try and correllate with sound.
This is almost impossible and one of the many reasons I don't use nor care about IEM's.

the 'signal' at the eardum differs substantially from the signal that enters the ear canal.
We actually hear 'better' at certain frequencies which only becomes obvious at lower levels, check the phon curves.

To put it another way...

When we listen to a piano its sounds reach the entrance of our ear canal (more or less bounced of the Pinna/concha depending on the sources position)
When we would place a microphone in the ear canal entrance the FR differs from the FR meaured at a few cm from our heads.
When we would place a microphone inside our heads replacing the eardrum we would measure a signal that differs substantially from that on the entrance of the ear canal.

Try listening through a thin tube and you'll hear it immediatly.
The sound on the outside of that tube thus has a very different FR from what's measured with an equally flat microphone on the inside at the other end of the tube.

The coupler used for IEM measurements has a mic that is positioned at the end of an open tube (open at one side)
Well not exactly like an ear canal which isn't actually a straight round tube but it bends, gets smaller and then bigger again and the eardrum is under a slight angle.
The coupler is just a small fixed diameter round tube with a mic on the end.

So when you want to find what how the outside 'sounds' like you have to undo what the tube has done to the sound, it has altered the FR (considerably).
That's the compensation needed son SPL on the outside is a copy of the inside mic.
We don't notice that change in the FR because our brain 'calibrates' the sounds by knowing/remembering how a real instrument/voice sounds.
That's also why we don't really notice our hearing getting worse over time untill we are confronted with ear measurements.
Our brains calibrate continuously.
When our hearing suddenly alters we DO hear it as calibration is a slow process.

Of course a tube that is open and 'listens' to the ouside world with a mic inside needs a different compensation than what would be needed if a soundsource is located halfway or partway down that tube and is blocked off with foam or stuff simply because the tube is effectively shorter AND sealed on both sides.

So when one uses the compensation that is required to compensate FR for outside noises (room or headphone sounds) you will need a different compensation than for IEM's IF you want the plots to show a correlation to how we would percieve it.
This means when a plot shows a 'flat' FR the SPL is equal for all frequenties which does NOT mean we experience all those frequencies equally loud.
How loud we perceive SPL with different frequencies depends on the actual SPL and the condition of our hearing.

That's why I mentioned when using OW, that is intended for ISO 11904-2 (on-/over-ear headphones) is used for something other than those type of measurements different compensation is needed than when the same artificial head is used for measuring sounds coming from the front, side or rear and needs to differ yet again.

Fact remains that the FR alterations that are created in a test rig need to be compensated IF you want to know what the transducer puts out.
Then, if someone wants they can also apply a reverse room correction to get a feel of how the same music would sound in a special conditioned listening room.

The raw plots of IEM's are easy to compare as they are all quite similar in 'microphone signal'.
Once 'corrected' all bets are off unless the exact same compensation is used. (that's what standards are for)
Correlating uncorrected IEM measurements with the actual sound is impossible to do and don't look anything like (corrected) FR plots of 'headphones'

You can also measure headphones on 'flatbed' rigs, in fact most measurements on this website (as well as mine and some on personal audio.ru)  are made this way and NOT at the 'eardrum' using an (expensive) manekin.
Sites like Rin's, Golden Ears, Personal audio.ru, innerfidelity, headroom and a few other sites DO measure using a manekin and some will show corrected and/or 'raw' plots.

To those not realising what plots they are looking at (compensated manekin, raw manekin, rawflatbed or compensated flatbed) will find obvious correlation between raw manekin and wrongly compensated manekin vs correctly compensated manekin (OW). OW on a manekin and flatbed have a much closer resemblance (for on-/over-ears).

Of course RAW manekin plots and raw IEM plots are comparable in a superficial way as they will both show the typical 'tube' effect but the over-ears/on ears will also have other effects caused by the skin/pinna/seal etc and the peak caused by the 'ear canal' will differ somewhat from that of the IEM measurements so even though the raw plots will look very similar they actually are NOT similar.

In other words IF 2 plots of on-/over-ear and IEM would measure exactly the same they would sound the same.. BUT an over ear and IEM that will put out the very same FR spectrum these will measure and sound different.

So in the end the question remains WHAT we want to see in the plot.
HOW 'average people' (whoever they are) perceive the headphone compared to speakers or not
OR if we want to see what a mic records but in that case we need to know the conditions of the measurement.
OR we want to see what the drivers actual SPL output is.

The latter (IMO) will be closest to how trained listeners perceive the sound when looking at FR plots.

So would it be safe to say that Rin and Tyll (or whoever) who measure using a an expensive and complicated manekin and then compensate for the coupler, artificial pinna, head, shoulder, etc using a standard do so with one (of possibly several) motivation being to give their measurements a sense of authority and adhering to standards that others are familiar with?  (i know, lots of assumptions here)

In Tyll's case the compensation he used differs from most others.
That is... IF he was to measure a headphone that has a completely flat FR (SPL wise) than it would NOT show as 'flat' in a plot. It would be sloping downwards from about 2kHz considerably. I thought (but Tyll or someone else correct me) that the decision to use a certain correction type was made together with the manekin supplier and isn't according to an actual standard but deviates.
Interestingly enough he 'converted' some of his raw plots (that are accurate) to OW in one of his articles. Fortunately some well known headphones and when you compare these OW compensated plots you'll find a better correllation with how they are perceived by many (certainly with me)
have a look: http://www.innerfidelity.com/content/first-test-estimated-harman-target-response-curve-various-headphones
having said this I often consult Tyll's more than excellent pdf's and once you know how to 'interpret' the FR plots they are more than useful.
Also the other plots and the neat (and constant) format sets a real example. Headphones can be compared quite well.
His measurement methods are well described and transparant.

Rin uses other, and later on OW, compensation that relate better to SPL IMO.

I frame it that way because I see threads where some do not acknowledge the validity of Changstars/Marv's measuring methods or lack of transparency of measuring methodology.

The validity of Changstar measurements is something that should be acknowledged even though home made gear is used that may not be openly discussed in one single thread but info is spread over various threads.
I think an effort is made to correlate measurements to how they sound and succeed as well, sometimes better and sometimes perhaps worse than Golden ears.
Of course most (if not all) of the guys posting their plots do so knowing their plots are indicative and not to be taken as 'correct' in an absolute sense.
As Marv often mentions... it's a hobby and you have to see the plots as indicative.
That's the absolute truth...

Please correct me on the following: as I understand it the thinking of the people who measure on flatbed do not use the traditional HTRF compensations because they believe a lot of the anatomical acoustic compensation is already handled by the brain,

I can't speak for others but even flatbed measurements need some correction but NOT the typical HTRF . I aim to measure the SPL coming of the drivers and suspect others try to as well. IF a speaker is to sound speaker like it should be tuned that way by the headphone manufacturer (or modder). This will (should) show as downward sloping on plots.
I don't know how others compensate/calibrate their rigs and can only say something about mine. The mic capsules I use (WM61A, now obsolete) are known to have a peak around 16kHz and they measure pretty flat even down low when in free air. A rig is NOT free air and the FR response alters when that same capsule is baffle mounted or infinite baffle mounted.
Knowing what the actual effects are I merely compensated for those 2 anomalies + the DAC/ADC/amplifier chain. The result should be a reasonable approximation of the by the HP generated SPL. I think it correlates pretty well to what I hear (may differ from what others hear).
Also when headphones are EQ'ed completely 'flat' on that rig they sound unbelievably real, not to me alone but those who heard it as well.
This too gives me some confidence it is reasonably accurate.

since they are after a qualitative relationship between FR and perceived sound it is more direct to just find the SPL near the drivers without the influence of pinna, canal, shoulder, etc. 

The jury is out on that. I have experimented with (crude fake) Pinna on a flatbed and various other obstructions/fillings/angles and do notice differences in plots taken with or without Pinna which also varies with the HP in question. The differences range between almost no influence to substantial as in several dB.
In general actual SPL is closest to reality.

And as long as you are comparing full sized to full sized, or IEM to IEM, the relational differences between FR's will give you a clear qualitative assessment of how the transducer will sound at the eardrum.

At the eardrum the FR of the SPL differs tremendously from the SPL that is present just outside of the ear canal.
We do not perceive the sound via our eardrum as if the eardrum is a flat microphone.
You could say that our brain compensates for the changes that are made by the ear canal.