Interesting glitch. TheZZAZZGlitch demonstrated that 255 boxes is theoretically possible
, so perhaps the Pokémon seen in Stadium 2 in boxes 13 and 14 would match up with the Pokémon seen in boxes 13 and 14 in Yellow.
The weird Pokémon doesn't surprise me.
Just to put things into perspective, they're probably other areas of the memory 'encoded' as Pokémon data; sort of like opening an MP3 file in Notepad. The game has to calculate the location of the data somehow, say the species, and for out of bounds locations it will likely correspond with an address that's used for something else.
A really simple example would be like this:
Pokémon 1: 64D1
Pokémon 2: 65D1
Pokémon 6: 69D1
End of list: 6AD1
So Pokémon 8 would be 6BD1
But this is actually used for the second species byte of Pokémon 1, so Pokémon 8 would show that. It wouldn't be 'nothing'.
The Pokémon base stats data (and starting moves, sprite data, etc.) structure is read like this (except for Mew):
0x0383DE + (DexNumber. - 1) * 0x1C
The last valid entry is Mewtwo, so the end of the data is at 3942A + 1B = 39445. But past 39445 the developers are free to put what they want. Missingno. happens to be located at 0x39FC2 (which is way out of bounds) because 0 underflows to 255, and if you look here
its data is actually Biker data read as Pokémon data.