My husband's says the same thing on the bottom of his, which he ordered from the registrar in the county he was born in. It concerned me at first as well, but I think really what the ECO is looking for is that your sponsor is British--not so much the identity as much as the citizenship aspect. In my case, we used my husband's long-form birth certificate and a photocopy of the picture page of his passport to prove he was British and there didn't seem to be a problem. But, I can't really speak as to whether an adoption order would act in the same respect--though in my unprofessional opinion I think it would, but I don't have any experience with that particular issue you have (hopefully someone has and can tell you for sure).