From 1985-1987, you could always tell the N from the R easily: the N cars had no grafitti and the R cars were the dregs of the system (grafitti splattered montage of R16/R27/R30/R32/R40/R42's). When the switch was made in late May 1987, the N still had some grafitti-coverd R32's before the R68's were fully delivered. Must've sucked to ride the Astoria line, seeing all the clean cars running on the "other" line.
A similiar split developed on the 2 D services, with the Broadway section getting new R68's and the Bronx/6th Ave. version gettng the awful R42's, pre GOH.