Thanks. Very informative.
But I think you left out one type. The early / mid-sixties which was very similar to the late 50's Spring Street you showed. Although there were no entire early sixties stations, there were numerous IRT extensions from 9 to 10 cars done during this period, such as extensions at Kingston and Nostrand Avenues. The difference being the tile was shinier and the lettering was white on a dark background rather than the other way around. It also clashes dramatically with the rest of the station and was built closer to the platform edge than the rest of the station, presumably to eventually allow for the entire station to be covered by this type of tile. Later extensions were built in line when it was realized that this would never happen. (Sorry, I don't have any photos and don't remember if the dark band was connected between the station names or not or even if these extensions still exist as they were built since I have not been back there in 25 years.)
The mid-sixties style is represented by the 57th Street / 6th Avenue Station and the Grand Street Stations which also used a shinier tile than the Spring Street type. Unlike the others, 57th Street doesn't have any dark band across the tiles.
Also, when the early 70's BMT renovations were completed (Prospect Ave, for example) I remember much criticism by architects at the time saying that the TA was covering up a treasure and that future archeologists would one day accidentally find the beautiful mosaics underneath. They stated that it would have mad much more sense just to restore and replicate the mosaics rather than cover them up.
Interestingly enough, we didn't have to wait for future archeologists to uncover the mosaics, because the TA realized their mistake in our lifetimes and actually started to remove these renovations and restore the original tile at most stations which were covered over just as the architects wanted them to do in the first place. I wonder if they plan to also "uncover" the 4th Avenue Line stations as they did with the Broadway Stations when funding is available.