In SPW, we have two major inheritances of martial arts which are not explained.
1. Ren Woxing practiced Star-absorbing Technique, which was described to be a hybrid of Xiaoyao Pai's Divine Art of Northern Ocean and Energy-Dissipating Technique passed on by a certain member of the Dali Duan family. It went straight from Northern Song dynasty to whatever time period SPW is in (most people believe it is Ming dynasty), thereby conveniently bypassing the 3 major novels in between DGSD and SPW, which didn't have any mention of Xiaoyao Pai or energy-absorption methods.
2. Feng Qingyang somehow got ahold of Dugu Qiubai's martial arts.
Can you think of any other instances of Passing of Martial Arts Through Time & Space Without Details?