YC Equity stakes are likely unable to be diluted. Not all shares can just get 'diluted' aka expanded.

We get diluted. Every investor gets diluted. They may have the right to buy more stock in later rounds to maintain their percentage, but they do have to buy it, at the price of that round.

Interesting

Nope, YC's equity gets diluted like everyone else's. In fact, while many investors will buy more shares (at the new price) to keep their % ownership, YC does not, so their ownership % when the company exits is probably 3% or less, down from the original 6%.