Reality quakes and timeline editors always leave behind those little clues to the former timeline's existence. You know, stuff like the famous portrait of Henry VIII holding a turkey leg (which no longer exists in the current timeline), or the series of children's books about the Berenstein Bears (in which the spelling has been altered in all the extant records and physical copies to the "Berenstain" Bears). Sometimes a lot of people have consistent memories of these traces of earlier reality, not just the privileged few PCs independent of the timeline shifts.
You can find a catalog of such possible tipoffs at
http://mandelaeffect.com/