I am working for the election board in North Carolina. The Poll book has a notation showing if the mail-in vote has already been received. And, we won’t allow them to vote in person if it is marked.
And, if they vote in person and then mail in the absentee ballot, when it is received it will not be counted since they already voted in person.
If they do vote in person and then mail-in the absentee ballot - they will be committing a class 1 Felony.
What do we do if we say we didnt request nor mail in a vote?
Of course that is why the voting in the dead of night is so effective, since the voting board members will know who hasnt already voted.