ZDoom

I've searched through every ccmd category on the wiki but it appears there's only a nextmap one. I'm guessing a previous map command is impossible, as you'd think it would have been implemented at the same time as nextmap, for competions' sake?

'nextmap' emds the map and starts the one marked as "next " in MAPINFO.
There is no 'previous' and the info is never tracked so there is no CCMD.

To GZDoom, naming maps "MAP15, MAP16, MAP31, MAP32" is no different than naming it "WOOD, TREE, LEAF, GRASS". Let's say hypothetically you are on MAP16 (or in this example TREE). If MAP15, MAP31, *and* MAP32 all lead to MAP16 (in our example, WOOD, LEAF, GRASS all leading to TREE) - how is the engine supposed to know which one is the right one?

Maybe it tracked the last map played - but then if you warp to MAP16 directly, you still won't know which map is supposed to be the previous one.

So basically you're left with a guessing game and a good chance for too much ambiguity.

Your best bet is using the "changemap" command if you want to keep your inventory, or the "map" command for a pistol start.