I too have no idea but the topic always interests me from the tracking/costing/organising changes perspective.
If an element is removed and later reinstated in the exact same place with exact same features is it the same element or a different element? These are always the issues: what makes an element the same element to the degree that someone cares about the difference? If I remove and reinstate it in five minutes probably nobody cares (it wouldn't be the same DB entry however). On the other hand if the time period is a month probably everyone cares, especially if it's something that shouldn't have been omitted in the first place.
If I go by UID and it is moved across the site is it still the same element by UID alone, no.
Like humans you need:
Location, date of birth, time of death, social security id (for fast ref). Governments have been tracking their citizens and other resources this way quite well (since Domesday Book). Tracking so few elements in a Revit model this way seems trivial in comparison.