R62s on the Flushing Line in the 1980s

I was recently looking through a great set of photos by "farrockawayatrain" and I found this photo of an R62 train from the 80s. I knew that some R62As (particularly lower 16xx) trains tested on the line during the 1980s, but I'd never seen an R62 photographed. Does anybody know how long this test lasted, and why R62As were later favored over R62s?

Note also the rare R62 rollsign in this photo--a few R62As (namely 1918, 2067, a 17xx car, and a 21xx car) have an R62 rollsign installed, but seeing the (7)'s destinations in that single-line, condensed script of the R62s is a rarity.