TPV for sale…

It interesting that the ad does not actually claim that it is a Terry Prince or RTV Egli bike, just that it "has the appearance and specs" of one.

That can only mean that the auction house has reservations, no?
Yes, it’s a strange use of the word ‘appearance’ but when put in context with the rest of the sentence I’d say they do not mean it in that way. They seem fairly clear what it is, and of it’s provenance:

“This motorcycle has the appearance and specs of an RTV Egli Vincent 1200cc Black Widow of which only 12 were built and going by the engine number it appears to be the last, the frame and tank are badged TPV making it The Only Terry Prince Vincent Black Widow ever built.
Purchased new from Union Jack Motorcycles in Melbourne“.