In may cases more than one man with the same surname, not all necessarily related, were each granted their own coat of arms, all different. No one peddler who sells them on the internet, at shopping malls, in airports, in magazines and at Disneyland will have all of them. They don't need to in order to sell to the gullible. The only time they will have more than one is if more than one man with the same surname from different national origins were granted one. Then they will have one of each and there might have been more.
Also when a man was granted one in Britain, all sons were granted one with some differences. Only the oldest son inherits his father's upon his father's death.
Anytime you buy one of those things and if it is valid and if you display it, you are guilty of usurpation of another man's identity. They don't belong to surnames and actually they don't belong to families. Poland and France might be the only European countries where they belong to a family but they don't belong to a surname.
What is so bad about their selling those framed coats of arms, sometimes they are mounted on a walnut plaque, is that a family history come with it and that family history will not be the same for everyone with the same surname. See some links below.