Thanks for the heads up Ian, I am well out of touch with the ever changing regs, though I suspect when you mention the term "Documented" I wonder at what level the documentation might be acceptable, thinking perhaps as a minimum recorded by a recognised restorer of the Marque or the marque club or perhaps more importantly the DVLA..? Thinking if a replacement chassis is fitted then the "original" numbers re-applied with a suffix perhaps, that the DVLA is notified of the updated "identity" applied to the chassis... or perhaps just drop the suffix and just number as before without informing the DVLA... yeah can of worms for sure..... Hmm..?
That which seemed acceptable in the past has altered considerably perhaps more so in the world of high value old cars, such as the Bentleys, more so if the law get involved...?