Most typically the door has been replaced.
If this is the case, no big deal.
If the vin on the dash match's the title but neither of those numbers match the cowl and radiator support, then you have a slight problem. The car was not original to your title. This is considered a re-vin and you have to tread lightly. If they state your in gave you a title after verifying the car with the title that's great !! However, when you are going to sell the car you should let the purchaser know that these do not match as that can really cause some problems. Mostly with the possibility of the body being stolen. Federal crime, Federal databases, fines, prison, etc.
I'm very curious now which of these boats you are in.