United sent me the requirements for my trip via email (negative test <121 hours before final flight leg to SXM). It's been my experience that airlines won't allow passengers to depart if they can't legally arrive. In fact, I need to present my documentation at the ticket window for my initial check-in. So I can't print a boarding document at home. United is covering itself.

So your airline will confirm to you what you now know.

Also, I am honored to be your new best friend.