> This l[e]d me done a rabbit hole on wikipedia:

> Advent calendars in their earliest forms were invented approx. 80 years ago.

Well, Wikipedia starts its "History" section in 1945, which is 80 years ago. But what it says about advent calendars in 1945 is that they were lower-quality reprints of earlier designs. This strongly implies that they weren't a new concept in 1945.

The German wikipedia is more interested in the concept and cites the word Adventskalenders to the novel Buddenbrooks, which features one set in the year 1869 but was published in 1901. Either way, the calendars were clearly an established cultural phenomenon well before 1945.

Looking at the talk page (for the English article), it seems that the history section was provided by a "translation group" from their translation of a matching section of the German article. It's not clear why they began with the post-war period; the German page goes back much further than that, which was also true at the time they provided their translation. But this does explain why the English "history" section begins by referring to prior context that doesn't exist in the English article.