I'd guess someone has reshelled a sapphire into a 3 door shell but, instead of doing it properly with an SVA test, a DVLA-issued VIN and an age-related plate, they have effectively rung the Sapphire VIN onto what may or may not have been a new shell.

You can forget any idea of FoMoCo building a 3-door in 1989 at any kind of expense. Once the lines are re-tooled you couldn't pay enough to retool for a one-off car, and they don't have the facilities to build a car off-line unless all development and prototyping was to be stopped for a while!