Citation needed? There have been one-off, incomplete iterations in extensions, but core and contrib have never had this.
> POSTQUEL allows users to save and query historical data and versions. By default, data in a relation is never deleted or updated. Conventional retrievals always access the current tuples in the relation. Historical data can be accessed by indicating the desired time when defining a tuple variable.
I looked this up during another thread which also has some other sources if you want to dig further: https://news.ycombinator.com/item?id=37956687