And the T1 example pertains to transit operators as much as it does to preservation.
No it doesn't, not remotely.
Not for the transit operator because the R110A is short, narrow bodied rolling stock designed to deal with the design of the IRT system, so you couldn't casually drop it into the TTC subway; and not for preservation, either, because if you went to a museum expecting to see a T1 and got an R110A, or vice versa, it wouldn't bloody fit the bill, now would it?
How about a fully intact and functioning motor (especially one attached to the bogie) from said vehicle?
Still no. How many transit museum goers do you think really care about the trucks and traction motors?
Imagine if the New York Transit Museum only had a collection of trucks. They'd be laughed out of existence.
I sure didn't spit at anyone's feet when I got to see the front end of H4 #5619, even though the rest of the car is long gone (the front end is the most notable component there anyway),
Not an example of preservation.
or all the times I got to see 5707, even though its propulsion (the most notable component there) is unfortunately gone.
Not an example of preservation.
They can be, sure, but just look at how the R62 was built on the opposite side of the world in Japan by Kawasaki, while the nearly identical R62A was built right here in Quebec by BBD (obviously not from scratch and very obviously based on the R62).
The R62A was specifically built under license from Kawasaki, BBD didn't casually evolve or copy the exact same design. In fact, the first 10 cars had their body shells built
by Kawasaki, and shipped to BBD to act as production line patterns.
The point is that while something can be customized to a specific system, at some point it's no longer a customized version of the original but just something else.
You're missing a couple of fundamental points here. All modern rapid transit stock is bespoke, so they are all going to necessarily differ from one another. And grouping a group of trains together doesn't in any way suggest they are all the same - it means they have a basic starting point from where the design begins, and then it's changed to meet the requirements of the operator in question.
Or are the Flexitys used for the Crosstown completely separate from the legacy Flexitys, just cause they look different? How about Flexitys in Europe? It's the same as your circular argument about whether funiculars count as railway vehicles or not. It would be nice if you stopped trying to break through open doors just because you don't agree with the way something is classified. It is BBD's product: they said that X group of trains are all members of the Movia family, therefore they are, even if you feel they shouldn't be. If you don't like it, find someone involved in promoting the product line at BBD and tell them they're wrong.
And since you bring up the T3 and PCC, it's well worth pointing out that these are another example of the same phenomenon. The T3 is NOT distinct from a PCC, it IS a PCC because its trucks and propulsion system make it so, even though the car body was designed from scratch. Same goes for the previous Tatra T1 and T2.