[gruez]

Source? I searched around and the first source[1] seems to confirm what you say

>you can only receive a certain number of rewards from each rarity level per 100 Pipe uses

but further down it says

>Additionally, as long as you haven’t exhausted the quantity by rarity for its category, you can receive duplicates of a reward from the Pipe.

However, it also says

>In fact, you’re guaranteed to receive at least one reward of each type by the time you’ve used 100 Pipe pulls — though the exact reward you’ll get is random for all categories except High-End Spotlight.

I agree that each roll isn't independent and you can't model it as such, but I don't think there's any mechanism to guarantee you a prize given enough rolls, and I still suspect the author messed up the math.

[1] https://www.gamerevolution.com/guides/600991-mario-kart-tour...