Some of what I am about to post may be off a little, so please feel free to comment.
The GE R10s lasted into the Summer of 1989. This much I am sure of. Although they were due to retire anyway, they were retired "early" due to a huge water main break around 42nd St and 8th Ave forcing suspension of all 8th Ave subway service between W. 4th St and Columbus Circle.
During that time the "C" operated as far as 34th St only. This enabled the TA to retire the last of the R10s because they didn't need as many cars to provide service.
This was an interesting period for a number of subway routes.
At first, all 8th Ave subway routes operated along 6th Ave. for about a week. This proved to be disasterous at best because of bottlenecking and numerous track switching which lead terrible delays, as well as mass confusion.
The following week the TA came up with this plan:
"A" operated between 34th St and Far Rockaway or Lefferts Blvd-the R44s provided 100% of the service (that was the summer from hell).
"C" operated between 34th St and Rockaway Park or Euclid Ave.-operated 10 car, YES 10 car consists of R10s, rebuilt and unrebuilt R30s and only 2 sets of R38s. They later removed the R10s from service.
"D" didn't have rush hour Bronx express service (not sure about this one).
"E" operated between WTC and 179th St via 6th Ave.
"Q" trains operated between 207th St and Brighton Beach from 6 am to 9 pm weekdays making all express stops only; and between 207th St and 2nd Ave nights and weekends making local stops-operated mostly R38s and a handful of R68s. In fact, during this time for some reason half of the lights were not operating in the R38s. Does anyone know why this was done?