I get asked as a matter of course to review sets of exercises by students trying to remember how certain forms look, and what goes in what set.
Of course there are formal sets, and 'right' ways to perform forms, but even over my years of training, differences have manifested from year to year. It drives some folks crazy ... "but when he showed it a couple years ago, it didn't look like that ... which one is right"?
Well of course there are many 'rights' which makes it very hard to say - 'The form is done this way, and only this way'.... which I guess is what people want to hear.
However, it's the principles behind the forms that are the important part, and in sets, that a spectrum of attributes are trained that create a whole.
It makes giving simple answers more difficult, and often my response is ... "Well it looks like this, but I've seen it done like this, and this too, by people I respect, and who knows, next year, we may learn it differently. This is what it is trying to teach you, and these are the principles to keep in mind .."
Hopefully by this point, the student's eyes have not glazed over .....
In my own training, I have learned differences between ancient, pre WWII and post WWII Japanese sword, changes in Tai Ji forms and other arts that parallel political and cultural eras, Bagua as it manifests in as many different ways as there are people that learned it (due to background, body type and personality), and am part of a Filipino lineage where change, down to the very NAME of the system, is close to mandatory from generation to generation.
WHY something is, is way more important than WHAT it is, as the 'what' is hugely dependent on the individual, the zeitgeist, and the audience.
Remember, get too fixated on the finger that is pointing at the moon instead of looking up, and you might miss all the heavenly glory .... :-)