As one who actually worked in building new guns in the 60s &70's ,it was common practice for shops to order guns ,[both with the name of the maker or their own name on], with heavy or full choke and the stocks left long,the butt end unfinished. When sold the gun could be altered to the customers requirements.
This raises the question of "originality" . Is it the makers records or the end users wants ,the length and choke he buys the gun with ,to be considered original?