When you click on ‘Today’s Posts’ you are presented with new posts. In the case of having a few pages to wade through, it may take a short time to wade through them all. In the intervening time, new posts may be made that are not part of your list.
It would be nice, if after viewing ‘Today’s Posts’, one could then select ‘Mark Forums Read’… and yet avoid having this include any new posts that were made in the intervening time I mentioned.