Now that you have the hull number, go to the USCG Web Site
and run it....See what Documentation Number is assigned to the hull number, which should help you in the long run dealing with this.
You are probably aware, but once a Documentation Number is assigned to a vessel it never changes, even if the owner registers the vessel with a State.
An example would be a Documented vessel is sold and the new owner registers the vessel with his home state instead of the USCG. 20 years later I buy it and register it with the USCG... They activate the orginal Documentation number not a new one.
Sounds like there has been a major paperwork mistake....