* SoulSilver is a Generation IV game: It only features Pokémon up to generation IV, which includes Pokémon from the first four generations (1-4). This means Pokémon from generation V and beyond (5-8) are not available in SoulSilver.
* The National Dex: While you can obtain a National Pokédex in SoulSilver, this doesn't mean you can get all Pokémon. It only allows you to see all the Pokémon available in the game, not all Pokémon that exist.
Sprite Differences:
* Generations: Pokémon sprites have changed across different generations. So, while you can find Pokémon from generation I in SoulSilver, their sprites will look slightly different from their original versions in the first games (Red, Blue, and Yellow).
* Regional Forms: Some Pokémon have regional forms, which are different versions of the same Pokémon that exist in specific regions. These forms may have different sprites and abilities. SoulSilver features a few regional forms, like the Hisuian forms introduced in Pokémon Legends: Arceus.
To get all Pokémon, you need to play more recent games:
* Games from later generations (starting with Generation V) have expanded the Pokédex and include Pokémon that are not in SoulSilver.
I hope this clarifies the situation!