Interesting Jan, thank you for the link to the earlier posts. I think we can safely conclude that this stamping is not of WD origin/purpose but is more something which had a purpose from/for the factories.
This BSA is a very strange mix of parts. The engine is not genuine Dutch Army spec, the timing side of the engine casing is missing the hole for the fitment of the oil tell tale. There are 2 options in my opinion: 1. the engine casings are a non-matching set or 2. The engine number is later re-stamped.
