Yep. The three-footer had differences from the 11-footer, and details of the 11 footer changed from shot to shot, and the Enterprise herself was represented by an AMT kit in Tribbles, and no one's going to argue it's a different ship class from itself. The AMT kit as the Constellation was meant to be another starship just like the Enterprise, and its inconsistencies matter as little as all the different versions of the Enterprise seen in a single episode.
I just like to think of
Constellation as a different class from
Enterprise because it gives a little more depth to Starfleet. *All* the other Starfleet ships we saw on the show were the same class as
Enterprise, so I just think it's nice to have
Constellation be something different.
There were the differences in the model itself, the registry that was much lower than the commonly-accepted registry of the lead ship of the class, and inside, I believe the set used for Auxiliary Control was different that what we eventually saw for
Enterprise.
Constellation even uses a slight variant of the registry font. All of these things together combine to give me the impression of an older ship of a different class.
YMMV, and I understand that this is a minority position. And of course, TOS-R went full-on Constitution class with
Constellation. (I would have actually played up the differences.) As far as the AMT model goes in "Tribbles", though... it was really too small to make out any details, whereas in "Doomsday" it was filmed up-close, and the details stand out.
Sure,
Constellation looks a lot like
Enterprise. But as a lay-person, I think a lot of different classes of real-life naval ships look similar, too. You could say the differences are all due to slight build differences within the class. I just think it makes Starfleet seem "bigger" with
Constellation as a separate class. And just going by the original version of the episode, I think either interpretation is a valid one.
