Because the data is collected while voting is ongoing, and audited after the fact.
This is how we know how extremely few problems there are, and how we catch the accidents (which are backed out, hence the delay between voting and election certification), and the fraud (which is extremely rare but of course also backed out).
This is how we know how extremely few problems there are, and how we catch the accidents (which are backed out, hence the delay between voting and election certification), and the fraud (which is extremely rare but of course also backed out).