Also, the Metal Gear secret password that could possibly be the reason NoA banned vowels from passwords.
(I recall the password was "FUCK YOU (... some personal message from one dev to another)" but even just the first word was enough to get SOMETHING.
(Metroid has a valid password ENGAGE RIDLEY MOTHER F***** but I'm almost positive that is just a coincidental valid "random" password. One whose binary representation happens to match the checksum test. It does nothing useful, as after the game verifies it, it jumps to invalid code (from tracing in an emulator, it seemed to cause the MMC1 PRG setup register to get set incorrectly, breaking PRG bankswaps.) On a real console, it crashes on a black screen. On an emulator you might get different results depending on how it handles invalid opcodes. Like I think FCEUX puts Samus in a glitched version of the Brinstar starting room, but scrolling doesn't work. Nintendo's emulator for GBA seems to handle invalid opcodes by auto-resetting.)
Even the JUSTIN BAILEY password seems to be incidental. I think the only intentionally programmed Metroid secret passwords are the NARPAS SWORD debug passwords.
Many, many Japanese-developed games thus needed their password systems changed in some ways for western release.
Just a couple examples:
Adventures of Lolo 3 (Lolo 2 Japan) for NES replaced the vowels with symbols.
Mickey Mouse IV for the Game Boy, shifted vowels out of the password character set, shifting numbers into the end so the same total number of characters was the same in the localizations (The Real Ghostbusters in NA and Garfield Labyrinth in EU, both western versions use the same censored password set). (that game has a lot of other localizations but you could probably write a LoL book on Kemco alone... though there's probably not enough of a demand to actually do that.