I guess what I'm asking: is this a NYC regionalism (is it American BALlet Theater or American BalLET Theater?) or an NYCB affectation, or something else entirely? What is common elsewhere in America, not to mention current and former members of the British Empire?
I think it's a NYC regionalism. When I lived for a while in the Midwest and the West Coast, the word was always pronounced with the stress on the second syllable. I remember a couple years ago a friend visiting from Milwaukee made fun of the "snooty" pronunciation we use here. (It's not just in the name of NYCB or ABT, we use it for the word in general.)