Some Fallout 1 only facts that were retconned later:
- Vaults are just vaults. No experiments or such bullshit. If your Vault has malfunctioned, please send a complain to VaultTec.com
- Ghouls are exclusive to Necropolis. Harold is not a ghoul but a FEV mutant.
- FEV supermutants are exclusive to California.
- .223 pistol is a unique one.
- Deathclaws are rare and elusive beasts. People mostly don't even believe they exist.
- BoS is exclusive to California. No Washington units or other bullshit. BoS was formed by US army renegades from Mariposa Base.
- No tribals. People didn't degenerate so much.
- No real-life weapons.
-
Iguana bits are actually made from human meat
- Caps as currency are set up by Hub merchants, so there's no logic in other states using caps too.
- PSI abilities do exist.
- There's no random legions of raiders that appeared out of nowhere: Khans, for example came out of Vault 15. Jackals came from Vault 15 too, but were cut from Fallout 1 - they appear in Van Buren, New Vegas ans Sonora. Vipers were cut and didn't appear anywhere else.
- GECK is mentioned only in manual and it's just an agricultural tool - no laser turrets included.