Original System: Unknown
The Atari 400/800 and 5200 versions of Pitfall II are known for having a second quest after finishing the first. While all other versions of the end after getting Rhonda, the Diamond of Raj, and Quickclaw, the Atari 8-bit ports open up a portal which takes you to a second set of levels full of new obstacles and a whole new set of treasures to find (and explaining how harry got out of the original cavern). Programmer Mike Lorenzen was able to put this second quest in the game due to having extra time to kill while waiting for the Colecovision and C64 ports to be completed.
The 8-bit and 5200 ports are virtually identical except
for one small difference. In the Atari 400/800 port the
trees have more branches than they do in the 5200 version.
This may point to the Atari 5200 version being the original
version but that's just a guess.