There were no "original" chassis in the 8000 range. The last Vignale coach known to me was numbered 7554. That coach was manufactured in 1974, but the car assembled with that coach wasn't assembled until 1976. The first Maggiora coach was numbered 9001, it was also assembled in 1976.
Chassis with numbers in the 8000 range are known in each case to have been re-numbered by the factory after 1976. What the factory's reasoning for re-numbering was ... we don't have documentation. We suspect it may have been an upgrade from one model to another. Chuck Melton the registrar is the only person who may have new information on this subject.