Isn't it more of "Pitfall!" has a set of 255 levels that are procedurally generated and the author spent a ton of time searching for the best seed that would generate the levels we know today.
It isn't as if you could have a map editor and adjust the levels or the order of the levels, though you could run the generation procedure to find new levels to your liking.
David Crane, the creator of Pitfall, explains it all very nicely in a GDC Classic Game Postmortem [1]. I'm linking at the relevant timestamp, but the whole video is pure Atari 2600 goodness. The full Postmortems playlist is quite enjoyable too. I particularly liked the talks about the original Deus Ex, Myst, Loom, Adventure, Marble Madness, Ms. Pac-Man, Paperboy, Lemmings, and more. I find these videos very soothing and nostalgic. Got to rewatch them now...
Take a look at Solaris. Another huge game with 48 sectors and probably the best graphics seen on the 2600, all in a 16k cartridge.
Quite a feat considering how horrifyingly difficult programming the 2600 was. Even the SDK was fairly barebones, basically a VT100 connected to a PDP-11 running RT8 and a 6502 assembler
