[South40]

They say purges less than four months before the election might leave insufficient time to correct mistakes.

And how much time would there be to purge illegal votes once cast?

[Beagle8U]

“And how much time would there be to purge illegal votes once cast?”

Once a vote is cast there is no way to remove an illegal vote.

[muawiyah]

Purging dead people and non-citizens doesn't violate anyone's voting rights so you can do that right up to and including election day.

The only area where there's a legal dispute concerns folks who've moved ~ and in some places they prosecute you for keeping a registration where you used to reside (if you run for public office).