The original Metroid is infamous for glitches and programming foul-ups. With producer Gunpei Yokoi no longer among the living I guess they don't have anybody left to interview about how the infamous "hidden worlds" in the game got there, exposed by the classic Metroid Database website years ago (back when there were only the 8-bit and 16-bit Metroid games, which amounted to three games!) You have to climb through walls to find them; they weren't supposed to be there!!!
As for the original Zelda, I'm pretty sure the old NES cartridge CAME with maps of both the overworld and like the first six dungeons--too much stuff is probably too hard to find without it!!! Especially in the second quest, which to this day I've never even PLAYED!