Vanguard doesn’t use S&P, because they wanted low fees and the license was expensive. They use CRSP’s index rules.

I checked and it looks like new stocks get added to the CRSP index at the next rebalancing, which is September. So, even the knockoff S&P adds it quickly.

BTW, CRSP was run by University of Chicago, but got sold recently to Morningstar, a mutual fund company.