Actually, this is sloppy staff work on the part of the General to whom the
orders were addressed, Daniel Harvey Hill. It was his aide, Major John
Ratchford who knew the orders were duplicates, and was careless with them.
The orders were opened, meaning they got to Hill as it was only the two of
them had the authority to open sealed orders from HQ. Regulations are
very clear on who can and can't open sealed orders, any courier with
opened sealed orders from HQ would be presumed to be a spy.
We also know what happened to DH Hill after Lee figured it out from
reading McClelland's testimony in the newspapers. Hill was sent to NC
to "recruit" while Ratchford was re-assigned to Hood out west. Lee's
chief staff officer, Walter Taylor admitted as much post-bellum in his
memoirs.