thanks... I tried the DISM and SFC commands (in admin mode / run). They didn't pickup anything or change the result of the fail for that update (other subsequent ones install fine). So I am in the slow process of a refresh. IF that doesn't get me out of it, I will then do a factory recovery image which I already had on usb drive and have used before (used machines).
It is currently up to / installed a 2019-11 servicing stack update (kb4504418), so perhaps it may eventually get there. The update system on these seems "funny" as you can run the checker but it finds nothing but if you leave for a bit and then ask for a shutdown, in the options, a "update and restart" option shows up sometimes as opposed to a "restart" only.