Here in NJ if a new code is adopted, you are allowed a 6 month grace period, if the project wasn't started. If a project was already started, then the project follows the NEC that was in use when the permit was issued. If your project was started under the old code, then you should follow the old code. If you want to update some of the building to the new code, then you should check with the AHJ. I feel that if the newer code is still just a s safe or safer than the old code, then the AHJ might allow the new upgrade. Either way, you should check with the AHJ to make sure.
