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I had a 15-hour layover coming in on Turkish and out on United.
They kept the luggage.
100% talk to BA when you check in and then reconfirm with a person at the Baggage Claim service counter before you leave the claim area.
They can look at the baggage routing in the system.
Turkish said I would have to pick it up but talked to the United service desk and they said no.
So I suggest you ask BA.