So far, we’ve gotten a new master every seven years (1997-2004-2011).
It would be more accurate to say we’ve gotten a new version of the SE every seven years, each time also being the movies’ hotly anticipated debut on the latest home video format. The 2011 version simply used the 2004 master and made the additional changes from there.
It’s also worth noting we’ve gotten a reissue of the 2011 discs every two years. This would make us due for something next year even if it wasn’t the 40th anniversary.