From Bulbapedia, the community-driven Pokémon encyclopedia.
Each location in the Generation II games has its own ID used internally by the game.
In Pokémon Crystal, the location header pop-up at the bottom of the screen only recognizes IDs 0x00-0x5F; all other values return garbage strings.
Pokémon caught in Pokémon Crystal record information about their capture. This value is blank (0x00 0x00) for Pokémon obtained in games other than Pokémon Crystal. If a Pokémon is traded to a Generation I game, this data is permanently lost; however, it is retained when traded to Pokémon Gold and Silver, despite those games not recording this data.
In Pokémon Crystal, the Poké Seer in Cianwood City tells the player where their Pokémon was caught, the time at which it was caught, and the level at which it was caught. In Pokémon Stadium 2, checking a Pokémon shows where it was caught, the time at which it was caught, and the level at which it was caught. This information is not otherwise available to the player.
In the Pokémon data structure, the met location is stored using 7 bits, so only 127 locations (0x00 to 0x7F) are possible.
- For all IDs not marked (unlabeled) in the table below, she simply says, "Hm… I see you met <Pokémon> here: <location>!"
- Any IDs not included in the table below use the same response, but since they do not have valid strings associated with them, the location name will be garbage text.
- IDs 0x00 and 0x7E cause the seer to say, "Whaaaat? I can't tell a thing! How could I not know of this?"
- ID 0x7F cause the seer to say, "What!? Incredible! I don't how understand how, but it is incredible! You are special. I can't tell where you met it, but it was at level <level>. Am I good or what?"
- IDs 0x60-0x7D and 0xE0-0xFD are completely invalid.