Most YC companies have at least two founders. Many have three.

PG's language here:

In the current YC batch, 16 out of 68 companies, or 24%, have female founders.

is ambiguous.

If we assume for the moment that the average YC company has 2.5 founders, this statement could vary between the 24% number quoted (when all of the cofounders are women) and 9% (where only one of the cofounders is a woman).

It'd be helpful to have that clarified.