Do those ballots have to be postmarked on or before Nov. 3?
They have ways of checking for that. The IRS does it.
Certainly something as important a matter as mail-in ballots can be checked for non-compliance to the law--assuming that the law does not allow voting beyond election day.
The ballots will counted as long as they are postmarked by Election Day.
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You can bet those machines will be smoking and on fire before the turn them off for the night.
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Post office is in charge of marking it
They can back date it if they want to
Or put dates on phony filled out ballots