It should include everything including signature verification on mail in ballots, and special attention to ballots with only the presidential line marked.
The mail-in ballots are separated from the signature panel - they become part of an undifferentiated mass of ballots, there is no way you can trace back to whomever it was that cast it. So, in effect you are running about 5M pieces of paper thought a scanner, and will find similar results. The evidence of large scale fraud would be found extrinsic to the received ballots they are looking at. It is upstream of the tabulation process. You would need testimony from parties involved, records of activity that facilitated the fraud - documents, e-mail traffic, cell phone records. In short the usual stuff you find in a criminal prosecution of financial fraud, for example. If the kind of fraud that we expect happened is to be prosecuted, the chances of assembling that kind of evidence in time to effect the election is close to zero.