When I was a kid, I figured this whole scheme out myself using trial and error -- and in Mega Man, it's just about impossible to get many of the combinations just by playing. I was extremely proud of my work, and submitted it to Nintendo Power. They totally ignored my genious.
Now, all I have are my porely written notes from the time, and not a coherent write-up. Fortunately someone else has done the same, and laid it out plainly for all.