Yes, state MUTCDs are valid and identified in Title 23 of the Code of Federal Regulations. After a new national MUTCD edition is issued or any amendments are made in the national MUTCD, all states have three routes to choose from within two years. They can adopt the new or revised national MUTCD edition to be applicable to state traffic control devices.  Alternatively, they can choose to adopt the national MUTCD along with a state supplement as long as it is in substantial conformance with the new or revised national MUTCD. The third option lets the states adopt a state MUTCD provided it conforms with the new or revised national MUTCD to a substantial extent.