Thanks Guys.
I’ve found the problem. The particular set of documents I was looking at have become re-named. They were in a format “minutes-04-10-27.doc”. Somewhere in the transfer they have become “minutes.04.10.27”. Because of the full stops, Windows doesn’t recognise them as word documents. It may be that the file transfer has messed something else up.
I dug out my secondary backup and that’s OK so I’ll copy that back to the master..