It may never be possible to know for sure.
Some states (like California) don’t bother to count absentee votes unless the margin of victory is less than the number of remaining ballots.
I have heard this argument as well. However, I'm not sure that it is valid. Wouldn't a ballot have to be counted if ANY issue on the ballot, not the just the presidential line, might be affected? It would seem rare that there wouldn't be at least one closely contested issue on the ballot that would trigger the count. I assume if a ballot is counted, all lines would be tallied.
Source please.
How can they stop counting ? There are a lot of contests on the ballot. Not just POTUS.