One thought on differences in a style. I've seen two examples of changes from one senior student to the next as they matured in the art. You can see this in Ueshiba's Aikido, as you progress from his earliest black belts (like Shioda) to some that came up after his conversion to Omoto (like Tohei). There is a dramatic difference in the Aikido they learned, and went on to teach.
The second is in my primary art, Nihon Goshin Aikido. Steve Weber (probably the most senior active instructor in the art) described how Richard Bowe (his instructor, the progenitor of the art in the US) taught variations of the forms to different students. This would have been fairly early in Bowe's teaching, so he might have been experimenting, he might have been teaching more appropriate variations by body type, or he might have simply thought the variations were all valid for the form. I don't know, but I do know that those early students took some of those variations and ended up with small, but significant, differences. All those versions are, according to the stories I've heard from multiple instructors, the way Bowe taught them.