Gosh, you're all making ME feel old, reading these posts.
I was born and raised in NYC. MY memories go back to when the IND was all R-1/9 cars, except for the "A" train which had the R-10's. Those were my favorites, though we lived a couple blocks off the Grand Concourse and Fordham Road and had to use the "D" train all the time. I never knew car 1575 existed until my high school days, and was quite surprised by a flourescently lit car in the middle of R-1/9 types. And it even SOUNDED like one of them!
The IRT was basically my stomping grounds. We moved to Flatbush, and my dad was a lieutenant with FDNY, so we went to a lot of different fire stations. I remember mostly the Lo-V types, but one time we were on the 42nd Street Shuttle, and somehow I remember something different -- could it have been "Composites"?? I'm talking like around 1955-1956.... I vividly remember one day when we took the IRT from Newkirk Avenue to the Brooklyn Library, and in rolled a shiny, brand new train of R-21's. Every other train was Lo-V's; we were quite lucky to get the same exact R-21 train on the way home. In my younger days on the IRT, I remember the only mixes you'd see were R21's and R22's in the same train; seemed like they kept the R17's separate then. I also remember seeing R17's on the Flushing line when they were still maroon and shiny as our family would drive from Flatbush to Adventurer's amusement park in Flushing.. Yet, I never remembered seeing the R12/14/15 cars there -- until the first time I actually RODE the #7 in 1963. I thought it was like visiting a foreign land, as the cars were "strange looking" with the porthole door windows, and strange shades of dirt compared to the rest of the system, and those "funny loop thingies" on the cab ends. On weekends, friends from school and I would ride all over the IRT just to see where it went. Funny we didn't do much riding on the IND or BMT though, I can't figure why as we were all train buffs.
The BMT as I remember -- never rode it much, but had relatives on East 17th & Beverley Road. We would always go to the Albemarle Road footbridge by the tennis courts over the BMT cut, and watch the trains. I remember plenty of Standards, and the articulated trains with the "1" on the front and always wondered "why" there was a "1" there when the IRT already had a "1". The relatives then moved to Ridgewood, next to the Myrtle elevated, and one day I ventured onto the el, rode the "Q" types (man, were they SLOW!!!) and then went to Broadway and the Jamaica Line. I discovered the "15" train then, and was REALLY baffled about those route numbers. Couldn't find any reference to them anywhere, I was only about 12 years old -- this was 1963. (It only took about twenty more years to learn the complete BMT number system....)
In my high school years (1964-1968) things started really changing. The #7 line got the new WF cars, so all those "odd looking" cars from there came to the rest of the world, the mainline IRT. That's when everything started getting really mixed up. The Budd R32's arrived on the BMT. Then in 1967, the BMT and IND "merged" and all o a sudden, up in the Bronx on the "D" train, there's R32's!! Then the R38's got delivered....the last "new" cars I would see actually brand new, as we moved to California in 1968.
I went back in 1979, saw LOTS of grafitti. In 1980, sw WHITE subway cars. And in 1985, lots of stainless ateel cars made in Japan, and the grafitti seemed to be abating.