Its a confusing one this. When Whiteshadow15 asked about these crankcases nearly a year ago I couldn't determine from the works records what the original engine number may have been. Whatever has happened to these cases happened a long time ago as a VOC member reported exactly the same engine and its numbers in USA in 1975 so its not a recent thing.
The initial assumption was could it be engine 5732 and somebody had "corrected" the cases to match a typo error on a registration document / title. The problem with that is engine 5732 was a Comet according to the factory records and still exists elsewhere.
Usually engine numbers get changed by owners for one of the two most common reasons, with a 3rd possible reason added which should make every every buyer cautious of doing their due dilligence before buying :
1. Happened a long time ago when the value of the parts was low and the owner notices the registration / title paperwork for the bike didn't agree with what was stamped on the bike due to typo errors etc. This was before matching numbers was an issue and the owner just found it easier to just restamp the metalwork to agree with the paperwork rather than get the paperwork / title corrected with the authorities.
2. Happened more recently, usually within the last 25 years with an aim to make non mating parts appear to be a matching numbers bike or to "upgrade" a Rapide to a Shadow or Lightning with the intention to fraudently increase the value of the bike.
3. The parts are stolen and so their true identity has been removed!!
Simon