One of the lingering mysteries in the Jin Yong universe is the origins of the Dook Goo 9 Swords used by Fung Ching Yeung and Ling Wu Chung in THE SMILING PROUD WANDERER. Who actually invented the technique in the specific form that we see in SPW?
For the purpose of convenience, I will designate the original concept of Dook Goo 9 Swords as invented by Dook Goo Kau Bai as "O9" and what we saw in SPW as "SPW9."
O9 was the original concept of Dook Goo Swords as conceived and practiced by Dook Goo Kau Bai himself, hundreds of years before the time of SPW. We don't know if DGKB left behind an instruction manual that thoroughly explained how the concept worked. If he did, and this is what FCY practiced and taught to LWC in SPW, then there is no difference between O9 and SPW9...they are exactly the same thing.
However, I doubt Dook Goo Kau Bai was the type to leave a specific manual behind about how his sword techniques worked. It's possible, but that doesn't sound like his MO. His MO was more like leave behind the artifacts (his special swords) and a general philosophy and let other gifted martial artists figure it out.
If that's the case, and O9 and SPW9 are different, then how did SPW9 originate? Did Yeung Gor develop it during or after ROCH times and leave behind a manual that FCY later found and mastered, or did FCY himself extrapolate and invent SPW9 based on his understanding of DGKB's sword philosophies, much as Yeung Gor re-created his personal version of Heavy Sword Technique (which might or might not be different from how DGKB himself practiced it)?