So I was getting confused myself while translating because there are many similar matchless terms, so I decided to do a clarification. I have gone back over all the chapters they appeared in to make sure I got it correctly.
Matchless Swordsmanship = overall term. The other matchless skills should generally fall under this umbrella. It is the Sword Saint's swordsmanship.
Matchless Heart Technique = The skill first learned from Biban and the one referenced most often so far.
Matchless Sword = sometimes referred to as the Matchless Heart Sword previously. Will now be consistently known as the Matchless Sword.