NWoBHM is NOT a genre. It was a movement that spread worldwide, sparked other genres and helped propel heavy metal music to the monster it is today. To try to define it within tight boundaries is foolish in the extreme. It was also not exclusively British - only in origin. There is no reason I can see that some of the European, American or even Australian bands around who heavily influenced the movement could not be considered NWoBHM. For the same reason, old school bands could easily be considered NWoBHM - Priest are a shining example, as are Black Sabbath and AC/DC. All bands re-invented themselves and their sound, the latter 2 with new vocalists. I would think of Dio as a NWoBHM band even though RJD was not British.