Sturmey has built 5-spd IGHs since 1966, but, and it's a big but, it's been several different designs over that time period. No single design has ever been built for multiple decades. The current (W) series debuted only last year. The previous "ball locking" Summit series came out in 1999. Prior to that was the Sprinter series that began in 1993, and before that was the 1991 StAr5 (arguably Sturmey's worst hub design ever).