>>33237335>Legendaries are known to only have one copy, themselvesThere are three Type:Null, Regis in nearly every region, and a smattering of reoccuring, which seem more likely to be separate entities than 1 beast somehow everywhere, especially the birds.
Not even counting anime, where we have 6 genesect, two mewtwo, a colony of Lugia, a family of Lati@s and one owned by Tobias as well as a second darkrai, and a third Latias owned by a Nurse Joy, and two Deoxys.
My rules on it is, if it's not banned from Battle Tree there's definitely more than 1 in in-game universe, they're just super rare. They ban 1-ofs because it's not fair to other trainers. They could go out on a ruin-diving epic quest like you did to go catch themselves a regi to fight your regi, but there's only 1 Reshiram.