SilverWook said:

I own nearly all of the editions mentioned.

Can you verify as per
DVDBeaver 2001: A Space Odyssey comparative review
http://www.dvdbeaver.com/film/DVDReview/2001.htm
"ORIGINAL WARNER VS MGM: The first unrestored release from Warner (not shown here) is identical to the MGM edition in every way except packaging."

that the MGM (1998) and Warner (1999) DVDs:

have this anamorphic main menu:

while only the Warner (2001) DVD:

has this cropped, fullscreen one: