Like I said, Talmudic disputations...
While not entirely persuasive, it appears to conclusively exonerate the Young Napoleon of the charge of responding too slowly to the Lost Orders find:
As McClellan’s army advanced on Sept. 13, Union soldiers stumbled upon a four-day-old copy of Lee’s orders in an abandoned rebel camp. Known as Special Order No. 191, this paper revealed that Lee had dangerously split his army into five parts. Three columns had converged on Harpers Ferry to capture the Federal garrison there, a fourth column was in Hagerstown, and a fifth column was acting as a rear guard near Boonesboro, Md. Historians have debated fiercely over when the Lost Order was delivered to McClellan.
In his landmark 1983 book, “Landscape Turned Red,” Stephen Sears asserts that McClellan verified before noon that the papers were legitimate, then exhibited his usual excessive caution and failed to move his army for 18 hours. To back up this theory, Sears cites a telegram that McClellan sent to Abraham Lincoln at “12 M” — which Sears says stands for meridian or noon — in which McClellan confidently informs the president that he has the plans of the enemy and that “no time shall be lost” in attacking Lee.Where this essay falls flat is in its assertion that Lee had almost as many men at Antietam as did McClellan. Nowhere have I seen that argument advanced. Still, useful grist for the historical mills.
After the book’s publication, though, the original telegram receipt was discovered by researcher Maurice D’Aoust in the Lincoln papers at the Library of Congress. It shows that the telegram was sent at midnight (the word was written out) — a full 12 hours later than Sears thought. D’Aoust points this out in the October 2012 issue of Civil War Times in an article entitled “ ‘Little Mac’ Did Not Dawdle.”