Certainly is worth a try however, and unless you can find anything listed under "Standard" (instead of under "Guidance") that states that the "ROAD CLOSED..." sign is invalid unless it is acoompanied by detour signs, then you'll be hard pressed to prove that you were not in violation. Also, the fact that Detour signs are Orange, means that they are informational signs and those, are not part of the "required" regulation.
You are within your rights to make as best an argument as you may deem appropriate though. Good luck, and let us know how it works out.


