The NEC is revised a year before the International Codes, which adds a year to the process when the NEC is adopted along with the International Codes which reference it.
Virginia has an Administrative Process Act which states how many hearings have to be held, length of comment periods, etc. We used to adopt new codes and amendments about 18 months after the ICC issued the new codes, but after the latest enhancement of the APA it takes about 3 years. The 2018 Virginia Uniform Statewide Building Code, which incorporates the 2017 NEC, became effective July 1, 2021, but plans based on the 2015 code could be submitted for permit for a year after that. I expect many other states have similar cumbersome adoption processes.