I realized as soon as I typed that that SEVERAL bodies that were in production in 75 remained so through at least 78. Newport/New Yorker (in one of their finest incarnations), B-body 'Doba, and a few others.
So I revise it to say nothing after 83 (I'll fess up that I kinda like the J-body Cordoba and the 81-83 J-based Imperial, too).