Just my interpretation.
9 Yang,
as written in the book, is a method of internal energy cultivation. From various snippets, we read that the "energy" can re-act against force applied to Wuji and protect him. It doesn't appear to have a specific set of moves to strike or defend.
QKDLY,
appears to have 7 levels of attainments. Wuji mastered them all except for 19 lines when he first studied it. He later mastered the 19 lines after getting the correct translations from the "Fire Tablets" with Shiao-Shiao's help. It appears to be techniques for reversing opponents' moves against them. It also seems to help Wuji comprehend and learn Martial Arts skills quickly.
Tai-Chi gong,
HSDS book translation mentions techniques, but not specific moves. I'm not certain if any internal energy cultivation is involved. It seems to use "circular" techniques to redirect opponents' force. More emphasis is placed on "re-direction" rather than the QKDLY's "reversal" emphasis.
Of course, these are Jing-Yong's fictional Martial Arts... without even rudimentary manuals that more modern writers sometimes develop for their books.
We have nothing concrete to base our opinions on... just a bunch of snippets from the books that are sometimes contradictory. Jin-Yong wrote his books in the pre-wordprocessor era, as serial installments for newspapers... so contradictions and mistakes creeps in when his memory fails him.
Another reason why it's fun to debate Wuxia "facts"...