In the past, certain forms were kept "close to the heart" as "proof" of how high up someone was in a MA "clan".
As such certain forms were never done publicly or if they were, they were changed so as to not be subject to "trademark infringments" LOL !
Sometimes it was because the current GM or elders didn't OK the public use of the form, other times it was to just protect certain parts/facets of a system.
Typiclaly this would be the case with high ranking forms, as for example the Iron wire of the "white crane" form in some Karate systems.
Certainly it would not be the case in the "base" or "core" forms such as SLT in WC or Sanchin in Goju.
Yet, at the same time there are many versions of many core forms.
Sanchin for example can be style specific in terms of the moves, the technoiques the breathing or all of the above, 100 styles 100 sanchin is an old okinawan adage.
None of them are the REAL sanchin, just as none of them are "FAKE" sanchin, they are just different.
Its the principles that make a form, not the "techniques".
Psalms 144:1
Praise be my Lord my Rock,
He trains my hands for war, my fingers for battle !