There are many ways to trace where ballots are printed. I am a fan of radio-isotope marking of the paper from the mill and/or the ink/toner. Even if you got the formula used to replicate it, the source isotope and decay compounds would be next to impossible to match to the date of manufacture. IE - if half life is 2 years and you print the ballots two months later, your isotope ratios will always lag a detectable amount. To my knowledge, matching an isotope and its decay compounds as a form of post-dating is next to impossible.
That said, the fraud that is being committed is rather basic. They claimed voting machines were down and had voters deposit votes into the "safe keeping" of poll workers who would "add them later." In some areas, it would seem additional ballots were filled out by poll workers to be tallied.
The fraud, therefore, would still work against this kind of countermeasure. It may detect fraudulent mail-in ballots, however.
There are only a few companies which produce the ballots and I would imagine they are under a degree of national government/defense/security control.
So we shall see.