When Dumbledore looks in the mirror Erised he sees his deepest desire:
>! Grindlewald

But before that the mirror shows the past when

>! Dumbledore and Grindlewald close their "blood oath"

In the Harry Potter books and movies the mirror is never shown to show the past. Is this a plot device as they had to show that important information somehow or is it a movie fail or simply an error in continuity?

Or does the mirror show the past of the person looking into it at any other time in previous books that I simply don‘t remember?

I know, that Harry sees his parents, but again this is his deepest need at that time and not a memory / glance of the past.