Jin Yong seems to have certain numerical hangups. In the CONDOR HEROES TRILOGY, he seemed to be obsessed with groups of seven: the Gong Nam 7 Freaks, the Cheun Jen 7 Disciples, and the Mo Dong 7 Heroes.
In DGSD, Jin Yong seemed fascinated by "fab four" combos: the Four Great Evils, the Four Royal Guardsmen of Dali, Mo Yung F'uk's four flunkies.
I wonder if Jin Yong selected these numbers for a specific reason.