Its not as uncommon as you might think for numerous reasons. Everything from people finding the biological parents, to people as adults finally letting their prefered parent's new spouse to adopt them, all sorts of scenerios. Quite a few orphans or kids who aged out in state sponsered foster care eventually get adopted by one of their foster parents or some other adult they form a bond with. It provides legal and emotional benefits to both parties.

__________________
Meddle ye not in the affairs of Dragons, for you are crispy, and taste good with Ketchup!