In the final LUK SIU FUNG story, LAUGHTER OF THE SWORD GOD, the main villains, at one point near the end of the story, took Sai Mun Chui Sheut prisoner (or so they believed; my view is that SMCS allowed himself to be "caught" so that he could find the missing and believed-dead Luk Siu Fung more quickly). The villains believed they had an opportunity to kill SMCS easily while he was their captive, but they demurred on acting upon this belief too quickly because first, they wanted to get their hands on his sword manual, in which supposedly SMCS had recorded his peerless sword technique.
I believe LAUGHTER OF THE SWORD GOD was started by Gu Long, but due to severe illness (which would ultimately claim his life), he asked another writer friend to finish the story. There are several problems with a SMCS sword manual that did not fit how Gu Long portrayed the character of SMCS.
1. First, SMCS did not have a sword technique per se, with set stances and routines. In fact, his "technique," such as it was, was the complete opposite of that: it was a read-and-react style that required allowing the opponent to make the first move so that SMCS could spot and attack the flaws and the vulnerabilities in the opponent's technique. Unless SMCS was in the habit of keeping meticulous notes on the flaws and weaknesses of each enemy technique he encountered, I can't imagine there was much to fill this so-called "sword manual" with.
2. As a corollary of the first point, SMCS's approach to the sword was something he intuitively understood, but was probably ineffable to others. Words probably would not be adequate to express how he approached using the sword...he just intuitively KNEW. Again, this is not germane to writing a sword manual.
3. It's out of character for SMCS. Can you envision him spending hours writing out a martial arts manual? That's not how the character operates.
4. Who would the manual be for? The son he abandoned? It's not like SMCS was eager to tell the whole world how his sword technique worked, even if he could. SMCS likely reckoned that when he dies, his sword dies with him.
So I submit that Gu Long himself would never have personally conceived of this bit with SMCS's sword manual, and that his friend introduced this idea without fully understanding the character.