I’ve flown both AA and JB both directions alternating carriers based on both schedules and pricing and I’ve never been asked for proof of return on either end, which stands to reason because I’m one of those people who likes to dot all my i’s and cross all me tees and I always carry a copy of my itineraries for both directions, jic. My fear - the one time I might not have them is the one time I’ll come across a totally over zealous and by-the-book CSR who will request them!