If I'm understanding correctly, the error made by Waukesha's county clerk is easily verifiable. She is not changing Waukesha's official return. She is announcing that the official return will differ from what was reported to the media and explaining why. The official return will presumably match the machine tabulation and the ballots which secured on Tuesday evening. This isn't a question of departing from the machine count or of dicovering new ballots.
Folks should look at it but I suspect that it will be pretty straightforward. Its not clear now that there will be a recount or that a recount would have much chance of changing anything.
On the other hand, the one thing that we have learned to expect in the past few months is the unexpected.