Everyone knows about the grace period, and everyone knows the confusion that grace period can cause when it comes to "hidden edits" that seemingly came out of nowhere.
My simple solution: add another database field to each revision which is just a simple Integer, and keep track of the number of times each revision gets edited within the grace period (not sure if this could be applied retroactively - probably not).
If the number of grace period edits is greater than zero, display a nice little message below the revision bar in the history:
Perhaps even link the "grace period" part to a page which explains what that is and why the edits get merged during those 5 minutes. This would ultimately be similar to the "edit count" that we already have for comments, which can be seen by hovering over the pencil icon next to the comment.