What I wondered most about is this...
Given that McClellan believed that Lee’s army was larger than his and also (IIRC) that McClellan believed the Lost Order was a forgery, why didn’t he at least take the time to have his cavalry check into whether the info in the Lost Order was accurate?
He didn’t.
And that in itself strikes me as negligence and incompetence. McClellan could have literally ran the Army of Northern Virginia into the Potomac if he had acted correctly.
The Civil War would still have dragged on but not for as long as it did.
If you think that’s negligence and incompetence, let’s reconvene on 9/18 and recall McClellan’s allowing Lee’s retreat from Antietam...