I thought that in times past, one of the requirements for US Documentation of a vessel was a proven "lineage" of all the past owners back to when the boat was new. But I believe that is no longer a requirement for US Documentation, and all you need to do is prove your ownership, and maybe (?) show the paper trail to the prior owner (not sure if you even need that).

(This in addition to the boat qualifying in terms of tonnage, etc.)