IMO "Advent of Code" only determines the timeframe in which it happens, not the amount of puzzles it must contain. It could just as well be four puzzles, one for each sunday of the advent, or any other amount, as long as they are released within those roughly four weeks before christmas.
Eh, the implication has always been that it's a Christmas calendar where you open one door per day until it's Christmas eve - just with code riddles instead of chocolate.
> one door per day until it's Christmas eve
That would be 24.
You also open one on Christmas. Some people consider Christmas more important than Christmas eve.
https://www.hallmark.com/house-and-home/figurines/precious-m...
That really depends on which country you're in.