You are right , is it possible to add it now?
I found the $ 10 bill on the sidewalk and did not have the ingenuity to plan for a foolproof way to find the owner , anyone is able to claim it as their own ... it's just plain dumb to ask the question from door to door because if you had the moral incentive to find the owner you also have the full obligation to find the rightful owner and this means inevitably doing more research and questioning the validity of anyone who claims the money to be theirs. You just may find that your neighbor is an ***hole.
And thus the question arises , are you creating more trouble by investigating the matter , since you might as well keep it for yourself - regardless of how much is involved - if you do not want to do a full proof investigation. And if you were to give it to the police , how would they really manage it , would they have the capacity to find the rightful owner?