All they really need is the audit trail of the printers. Each printer produces tiny code dots identifying it. If ballots originate from printers at locations or from people unauthorized to print them it’s a bust.
Every printer or copier that can legally produce a ballot will be easily traceable. Every ballot that originated from a printer that traces to Schwang Jiang Slave Labor Collective (X) will be Void. Any ballots produced on clandestine printers will not have identifying marks.
The only hurdle I see here is what happens if they’re already tallied and uploaded and if that poses problems. If that is an issue the assignment of electors can fall back to the legislature.