Any ballots that were printed in the local county election offices (versus from the big printing vendors) will be immediately identified.
Unless they were able to use the exact same printer, and back-date the printer clock, it will show -
The exact printer used
The exact time and date printed.
What happens when large numbers of ballots are shown to be printed in the early morning hours of Nov 4???
The huge batches of mail-in ballots are supposedly printed by 3rd party vendors using industrial drum printers from large rolls of paper that probably already include the watermark.
It's not clear that any batches printed by the local county offices would have those same characteristics.
Or that those local office would be clever enough to know to backdate the timestamps on the printers.
How many are even aware of the microdots?