John Sykes III
Maybe or maybe not. Several of the car builders had proprietary parts such as doors, ends and roofs. ACF and Pullman Standard come to mind. Also, some of the smaller builders got more than just the ends, roofs and doors from vendors - I have an add from Youngstown that extolls how they supplied the car side panels to PFE for some of their new steel reefers (I think they were R-40-25s). Plus a lot of PFE R-30 reefers had Bettendorf underframes. Bettendorf trucks are used the way we use the name Kleenex today (more correctly they should be called Bettendorf-style trucks). AAR took the best features of Bettendorf U-section trucks, married them with the best features of PRR 2D-F8 trucks and they became the AAR Type-Y or trucks.
Then there are items with trademarked names, like Dreadnaught and Murphy - trademarks of Standard Railway Equipment Company, the owner of which happened to be named William Murphy (not sure of his first name). SREC still exists as "Stanray" after their X pattern roofs.
One other glitch. Some companies sold licenses to other manufacturers, so Barber S-2 Ride Control trucks begat ASF A-3 trucks, etc.
The list goes on and on. I'm sure some of the others here will chime in with more examples.