I have come to realize that there are many many variations for each move in brazilian jiu-jitsu. Maybe there are too many for someone to master them all in a competitive environment. At the same time, I believe that one should practice whatever move the professor or instructor shows in a particular day, not because you have to master them all, but because you have to know what is possible with a given set of grips. For example, I didn't know the bottom of the lapel can be used in so many ways up to now : It's truly unbelievable.
So I have come to the conclusion that I should refine what I already know, in order to get better. For example, when doing the knee slide pass, I am now using a different grip than before, and it seem so to help in flattening the guy out for the pass. Progress isn't as obvious as when I was a white belt, but on the flip-side, my jiu-jitsu is getting more focused, more precise, more predictable and more controlled.