A reader pointed out to me this deterministic error I made in the post High-Water Mark, part seven:
There would have been a battle of the gaps at Fox's and Turner's whether or not McClellan found the Lost Orders – they would have flowed from a meeting engagement and from Longstreet's orders. They would have happened about when they did due to the tempo of McClellan's advance prior to finding Lee's dispatch.
Sorry for the verb agreement problem; more importantly, this should read, "There would have been a battle of some sort in or more likely beyond the gaps flowing from a meeting engagement." General Hill was not, as was pointed out to me, obliged to cover Longstreet's march to Hagerstown by defending South Mountain.
I'll write a little about historical contingencies later this week.