I disagree that the version of 2001 we have now isn't the "true" original version simply because the premiere (one single screening) was a different cut of the movie.
It's the version that first gets widely released to the public that should be considered the original version. That's where this argument begins and ends for me.
To further drive this point home:
When Kubrick restored 2001 in the late 90's he did exactly that - restore it. No changes were made to the movie itself AFAIK. I finally got to see one of the 70mm prints a couple years ago and it looked and sounded amazing, beat up though it was in certain sections after more than a decade of running through the projectors.