Thanks for these explanations @sam !
This doesn’t seem “that bad” (I guess everybody can understand that the count includes deleted posts). Now, I have some troubles understanding how this lead to what I witnessed. For example with the last “92 unread posts” I got. I don’t think there were 92 new posts created AND deleted between two of my visits.
The big question is: What happens when the difference between (highest post number - last post number read) is NEGATIVE ? Isn’t the system currently showing the absolute number of that negative amount as unread posts ? If yes, this is just what would really need to be corrected: Do NOT show any negative number as unread messages.
The problem would be when “highest post_number” gets actually smaller than “what post_number you read up to”, because the last or several of the last posts were deleted. As long as the last post of the topic isn’t deleted, there shouldn’t be any problem according to my understanding of your explanations. In my above example, I believe we may have gotten to “highest post_number” = OP, because everything was deleted except the very first post of the topic.