One of my counter did exceed the older value, let's say within the last two hours and no change.
The only way I can see that happening is just by timing... when the most online code grabbed the session data, maybe at that time a visitor disappeared? Not really sure, but I do know that sometimes XenForo's online counts can be off by one and you have to refresh to get the actual number of visitors. That is normal behavior because of when the session data is saved, I believe.
Only when exceeded not tied?
Only when exceeded. I could modify it to update a new date when the old value = the new value. The reason I didn't add that is because on smaller boards, the tie value may be set a lot, so that would mean a lot of writes to the registry.