Just my two cents so please don't take this wrong. If you are still what you consider yourself a new grower, there are many strains which are difficult to grow properly. You have 12 strains under your belt but how long growing? I believe that if you were to spend more time with each strain you would find they aren't as hard to grow as you might think they just don't fit into a custom feed program. What I mean by this it that if you are using some of these scheduled nute programs these plants just might not fit that program.
You might call me a slow grower, meaning that anytime I grow a new strain I grow it out first single cola with my standard soil and nutes. Watching the plant grow and respond to what it is given and looking for hints of what it might be missing in its' diet. Your soil might be too hot for a strain or really lacking in something each strain needs more of. I clone this first plant of the strain as early as I can so that I have another plant of same strain following closely behind the first, this gives me a point of reference and make the necessary adjustments for the new grow. By the 3rd or 4th time through a strain you can begin to understand what makes it grow to its' potential.
Hope this helps some, good look with all of your grows.