I was recently on an R62A where the conductor specifically pointed out that you could ride around the loop to the uptown platform, and to stay within the cars as the train went through the loop. I've also been on R142A (6)s where the conductor keyed the mic in the middle of the "last downtown stop" message and started shouting "LAST STOP NO PASSENGERS THIS TRAIN IS OUT OF SERVICE", when the train was just going around the loop to the uptown track, in service. It's more about how the conductor's attitude is than what model of train you're riding, really.
That message was pretty long, though. In my experience, it was sometimes to the point of having trains dwelling a long time in empty-ish local stations, or having conductors rush the computer to the doors-closing message. Generally, seeing the diamond on the front sign, or the map LEDs having the Bronx stations lit, or the next-train system showing instead of would probably be enough to determine whether it was gonna be Bronx local or express, so it's fine if the train says "This is a Bronx-bound 6 local train".