Here we go again!
This will be routine in close, hotly contested elections with operatives who believe they can acheive political goals via weak election procedures.
The "found" ballots might either be fabricated and introduced into the mix for the desired result, or be ballots believed to be in the opponent's favor that were "inadvertently stored in the wrong closet" - as may be the case here.
The sensible thing will be to produce serialized copies with strict depositing controls. There would be no ballots to be later found.