Addendums should be free, they make a cock up every time they issue a new edition or an amendment and they have to put it right.
For once the septics have it right. NFPA-NEC is issued on a three year cycle.
Where it goes a bit wonky is each state legislature has to approve the codes. Some states are nine years behind. Individual states can veto sections of the codes so AFCI’s are required in one house but not next door?