Did the returned ballots get imaged by the USPS sorting equipment?
If so, how long are those images retained?
Does the OCR meta data get stored with the image?
If so, those images with the meta data can be used to generate:
1. A list of ballots delivered to each election return address
2. For each of those County Clerck's offices, who actually returned a ballot via USPS.
Compare that against the "counted" mail-in ballots to flag the frauds.
J