Firstly, I think I can verify which is the last Mk3 made because I have the original MK3 despatch book. I have several original despatch ledgers, late 750/850 era. These are NOT on the microfilms existing elsewhere. As far as I know- but I will verify with Nick Hopkins- the story about Andover Norton actually building bikes in 1978 is one of many myths. They did have a cache of Mk3s off the liquidator in Wolverhampton, that they sold off one by one at slowly increasing prices for several years. I guess people who saw the new machines at Andover Norton THOUGHT they were being assembles there, not realizing they were just mothballed bikes from production days.
"New Nortons" are being built using part new, part used components, so "new" is relative. The last 100% new Commandos were, if my information is correct, the last bikes built in Wolverhampton in1977.
Joe