Galaxian, as seen in this 'set 2' release, provides another insight into variations within a single version. Building upon the original Galaxian concept, set 2 could introduce adjustments in gameplay mechanics, graphics, or difficulty settings.  Further research is required to delineate the specific changes from set 1 or other variations of the title.

Galaxian (version, set 2)

Galaxian (Recreativos Franco S.A. Spanish version)