Hi, scartacus!
Not sure about this one ... if they simply reprinted the same artwork for each release, then it's down to the 'feel' of the paper ... I don't recall any detectable difference in the actual content of the artwork.
There is a commercial reprint using the same artwork, but that's identifiable by being undersized. Yours looks like the full 30" x 40" theatre-used version.
Sorry not to be more helpful.
Best wishes,
Terry -
www.quadbod.co.uk