on Sat Nov 16 19:53:01 2019, in response to Re: Mixed Trains on the IRT - When Did it Start?, posted by Fisk Ave Jim on Sat Nov 16 17:57:44 2019.
IRC, it started as soon as it was needed since the cars were designed to run together. That was long before the R-12/14s & 15s came from Flushing. Those cars really stood out in those mixed consists with their different car design.
Does this stand out enough ? R-12 Museum Car #5760 before preservation.