Of course you pull your punch back when you miss. The question is do you pull your punch back when your fist hit on your opponent's head?
In the following clip, I don't see any pull back punch in those knock out punch.
I think they only go all out when they know they hurt the opponent and it's not going to miss. Like when you first feel the opponent out, you pull back. Then if you land a good punch and the opponent is dazed, then you don't worry about missing.
Below is just MY EXPERIENCE.
Like I said, I don't feel I have less power with the punch that I intend to pull back, it's all about practicing over and over and over and over. Takes MONTHS. 3 years of TKD, went to the school 3 hours before class practicing on the heavy bag, HALF the time on punching alone..........Still months. AND you can lose it. After I quit, I still practice at home with heavy bag, because I was not thinking and just going through the motion, I lost it. It's only lately after GowGa wolf reminded me to practice in slow motion, I started from the beginning. Still, it's been two months, still working on it.
You know when you get it, all of a sudden, the punch is effortless, the fist start penetrating the bag deeper, the sound is different with an echoy sound. You know when you get it. I think they call it Chin-gu-chi or something in Japanese. All the sources focus into one split second to a point.
Obvious other people have their own way, like I showed Chuck Liddell, I don't even see how he generated so much power, but he did!!! So he found his way of punching.