Not much to report; 3 more disks scanned and everything OK. Total 64/64.
One handy thing about doing this is that at least I now know with a pretty high degree of certainty what Workbench disks are original. I have got a number from eBay and indeed from my own original collection but could not be sure if I had written to them at all. So when I find, say, 3 disks with the same hash I can be pretty sure they are as original as the day they were first mastered!