in reply to the question of NEC 90.4,and the Montanna adoption of the NEC code,NEC is is specific in its wording and implication previous adoption of the NEC,so in their case yes they should go back to whichever was their last NEC book,although it would be outdated,setting themselves up open legal ramifications if things went wrong some where,yet if they had gone to the previous version before the current version ,their case and workmanship would be more in line with a logical approach.
Question:do AHJ's have to accept NEC?
Question :why are the different AHJ's not all on the current version?
I think the mere fact that they are in fact using any version of the NEC makes them obligated to use the most current version,I.M.O.
AHJs can accept the NEC any way they want. I don't know of any place in the US that doesn't accept the NEC, but there are many places with their own requirements. Some places were requiring a manual dc disconnect on the roof that wasn't required in the NEC. Also, if you have a better idea that the NEC, you can find out if they will accept it. It is up to the AHJ to interpret the NEC and they can interpret it any way they want.
We usually think of the building department as the AHJ, however the utility can also be called another form of the AHJ. There can be many different authorities.
To more specifically answer your question, do AHJs have to accept the NEC? They don't in France.
Any why are all of the different places not on the same version? I think it comes down to the way these "United States" are organized from 13 different colonies looking fir independence. The states wanted to keep their individuality and Boston and Virginia had no interest in telling each other how to build things. They formed a union to keep out the Brits. We still keep that attitude and every government entity likes to have their say, down to the city or even the electrical inspector. There are benefits to this American individualism and drawbacks. If is difficult to have a national energy policy with every state keeping its right to adopt whatever version of the NEC they see fit. Many states adopt different versions within the state.
Many other countries have a more national policy. I agree, it would make more sense to have a national electrical code policy, but California wants to wait 3 years to adopt and Massachusetts wants to adopt the Code right away.
At least we all drive on the right side of the road here.