Here's the deal: Overseas voters (typically in the military) receive special absentee envelopes that don't match up with the standard form that Minnesota uses. But Duluth has a policy of taking those overseas ballots after they receive them from the county, and then putting them inside standard Minnesota ones, filling in just enough info (name and address) to sort them out and get them delivered to the precincts on Election Night.
Thus, the county believes that those unsigned envelopes were in fact valid votes, that happened to be put inside envelopes filled out by county employees. County elections director Paul Tynjala just told TPM that he's confident the 60-plus envelopes he's seen were all in order, and the county is pulling the originals just to double-check.
It's probably correct that somewhere out there are votes let in on Election Night that shouldn't have been. But it turns out the Coleman campaign is shouting this from the rooftops based on evidence that is inconclusive at best, and horrible at worst.
And even then, there's no way to un-count absentee votes that were separated from their envelopes -- it comes down to the secret ballot. What this really is about is building a case in either the court or the public arena that a result with Al Franken ahead is not legitimate.