Indeed, so I would argue that it would be less divisive to draw a line under it, and say that if an aircraft is built from less than a specific (to be determined) percentage of its original parts at the time it left service, it cannot aspire to an original serial number. When I was working in the industry, every aircraft we built could be easily traced back to having significant original material. That is much less the case now.

All of that said, if it is well documented anyway, does it matter? In the case of the Spitfire Survivor books, it is a simple task to determine which aircraft are less ‘original’ than others.