*sigh
There's a sticky near the top called "Third Edition Changes"
Consider the following scenario:
YG and XLN disappear from wulin with the Condor - they are never seen again - despite GX checking the tomb and the valley.
Therefore they probably went to Dugu's lair which GX doesn't know about - they turn this into a home.
During this time they either discover a swords manual - which XLN trains from (YG cannot do so as he only has one arm) or XLN (with instruction from YG) develop the Dugu sword stances from Dugu principles (and therefore credit this to him.
Condor eventually passes away - and they move back to the ancient tomb - where they raise a son - who has a daugther who becomes the yellow dress maiden.
She inherits various martial arts from her grandparents (perhaps via her father)
If we imagine that YG and XLN live as long as ZSF in age terms - then by the time the yellow dress girl meets YG they may have only passed away within the last 20 years or so!!
Also if the dugu stances were made by dugu himself - this is likely to be the time when he used his violet sword - he himself then chose the HIS (dragon sabre) as a progression because of simplicity - therefore HIS should be superior to the dugu stances.
Even if JY later says that LHC is superior in sword art to YG this isn't necessarily a contradiction - because he has lost an arm of course his swordplay is not so exquisite (even if he knows the same stances). YG physically can no longer perform some sword stances - even if he knows the theory. This doesn't mean he wouldn't win a fight - swordplay and sword art is a factor but the brute force and simplicity of the HIS utilises the same underlying principles - force your opponent to defend by attacking. Brute force using the HIS is not graceful swordplay...
Yes, I am also wondering about this question since the series SPW is on now.