Tudor was founded by Rolex's Hans Wilsdorf to sell Rolex-cased watches at a lower price, which is exactly why its vintage market is complicated: many old Tudors sit in Rolex cases with Rolex crowns and Rolex bracelets, and telling a correct period-original watch from a later assembly is the real work.
Modern Tudor is a different proposition. Since 2015 the maison has made its own movements, and current production has its own case and bracelet identity. Counterfeits of the Black Bay exist and are generally poor.
The two reads that matter most are the movement — which should be what the reference specifies, whether an ETA base on older modern production or an in-house calibre on newer — and, on vintage, whether the case, dial, hands and bracelet all belong to the same period.