I understand what you’re saying Cboldt... They’re only looking in the pile of Cochran votes.
You’re right, they’d need to find the full margin of fraudulent _Cochran_ votes.
I stand corrected !
Well, there is no way to know if the vote went to Cochran or McDaniel. A reasonable assumption is that they are assigned AT LEAST in the same proportion as the total outcome; a majority of them for Cochran. And it isn't much of a stretch to assume that 90% or more of DEMs who crossed over to vote in this runoff were motivated by Cochran's GOTV effort.
At any rate, you need a number of invalid ballots at least as great as the margin of victory, to bring the outcome into question. That amounts to an assumption that 100% of the invalid ballots were cast for Cochran.