If you look up a Type certificate, the FAA clearly indicates the model of an aircraft as a 150, with a 150M a different model. It doesn't matter who is right or wrong, it isn't each FSDO's deal to prove anything about themselves. They represent the FAR's. We all know a FAR can be twisted this way or that to make it make sense to your application.
Each model of aircraft (say 150 since we are talking about the 150) is equipped differently. Different materials, instruments, engine, prop, Etc....all have different parts from model to model. Just because I have a certain prop on my 150 doesn't mean I can just swap parts with another (any model) 150.
The only true 150, is the first model built. It was built for 3 years. In 1961, it became the 150A. The only way the endorsement would be "legal" is if the training was done, and the student is authorized solo privileges in a 150 built before 1961. Blame Cessna, not the FSDO.
On a more extreme side, the P-51 A is different than a B/C, and different than a D. Just because they look alike, they aren't the same airplane. These are all P-51's, but that is where it ends.
If you still think its wrong, look at published ref speeds over time on the 150. I haven't looked, but I will bet they are different from model to model. I know for sure the 172's have different Vx and Vy speeds over different models.