I agree with trying to get it pulled where he is, before shipping. Odds are low he’s positive, but it would be such an enormous stress if he is and you only learn that after getting him home.
When I vetted my event horse (who was the price of many chainsaws, though less than half the price of one of those chainsaws they attach to helicopters!), his Coggins had just expired and the seller gave me a bit of a hard time about wanting to wait for it to come back negative before going through with the sale. The vet, who knew both of us, was on my side. Side note: I also learned when I asked for vaccine records that he hadn’t had any in years because “he got lots when he was racing”…six years earlier. This was not a money issue either. It was very weird.