I worked for 15 years for King County (Seattle) in the computer department and served for many elections. It was a ton of fun, fascinating to watch, and great to work with so many good people. Here’s how it works:
Counting the ballots on election night is purely theater, a show put on for the benefit of the media, mainly, and the parties and organizers for candidates and the issues. The idea was to get a reasonably complete and accurate estimate of the results as fast as possible to satisfy the public and interested parties. That pressure was exciting and fun, but it was terrible for accuracy.
For that reason, the results on election night were meaningless. We were allowed 2 weeks to do the job right without the glare of the TV lights and the crowds of reporters. The results of that effort were submitted as “final”, and could differ a lot from election night.
States have about a month to get the finals for the presidential election. And they’ll take all that time to get it right.