Has to do with the rules for the legal games:
• Expansions, DLCs, or anything of the sort will be included with their base game, so you can't list those separately.
• Remakes, remasters, definitive editions, or anything of the sort should also not be listed separately from their original release.
• However, certain remakes that differ from the original significantly are allowed. This includes, for example, the Resident Evil remakes and the Metroid remakes. This works on a game-by-game basis - if you're unsure about a specific title, ask me!
The separation is sure as hell subjective, but I think mZuzek is open to discussion if you want to treat SoulSilver/Heartgold as different games or the Demons Souls remake as the same.