Thanks, Peter, but I don't think I have read them as the missing posts seem to be at the end of the list. When I return to the first page of the "unread messages since my last visit", the posts that I have read are still there. [BTW: your reply did not appear in the list of unread posts or at least I didn't see it.]
This just happened again today: Three pages with 49 posts when I logged on. By the time I got to the third page, there were only 45 posts and I think I have read more than 4.
It is no big deal; I was curious whether I was missing any posts of interest.