I'm not sure of all the risks, so I played it safe and didn't register with a complete VIN.
One risk could be that with a vehicle description (and pictures) and VIN, someone could transform a Catalina into a 2+2 without a lot of investment and effort. With current technology, I doubt that it's difficult to copy a VIN plate. So PHS documentation would support it.
I think it's possible now to get close to a complete early Camaro, Firebird, Mustang, etc., with nearly all repro parts, starting with a body from
Dynacorn. WIth a vehicle description and VIN, it might not be difficult to build a reasonable fake. I don't know how good the bodies are and whether they have intentional differences from the originals. And of course it would cost a fortune. So this is different from the situation with 2+2's, but I think interesting.