I am genuinely perplexed how news outlets are calling these house races.
Where is the data?
In their wallets.
they use results from precincts that are in and exit polling, so if a precinct that is expected to vote for the dem goes even more for the dem than their gop precinct they can project
If you know the demographics and vote history of precincts that have reported results then you can use that to project other precincts that haven’t reported results yet.