Although some novels are only a few centuries or decades apart, very major changes in wulin seem to have happened and cemented. New sects rise in power, having their own set of martial arts and traditions and idols, a little too quick. I personally think Jin Yong packed his universe a little too full. Some sects that are stated to be hundreds of years old aren't even mentioned in novels that take place a few hundred years earlier. And a few hundred years later, no traces of it remain. This is especially true in the novels that have little to do with each other like SPW, OTG, DOMD, and FFSM. Whereas major organizations like the Beggars Union, the Duan family, and Shaolin are found throughout DGSD and the Condor trilogy, novels taking place in later eras all have sects that are unique to them, but still have centuries worth of martial arts and traditions.