It is possible that Tom has acquired the property by adverse possession, but several elements must exist in addition to the required statute of limitation. For this reason anyone in this situation needs the advice of a good real estate attorney. For example, depending on the State statute the fact that the possession ocurred due to a mistaken survey might work in either parties favor. If Tom was possessing someone else's property and they didn't know it, was the possession "adverse." As you can see determining the answer to a question like that could get complicated, and is what keeps attorneys in business.