As someone who went from Gen II to Gen VI. Can someone explain the Gen IV Pokedex.

I am going back and playing the games that I missed out on. However I am so confused on how Gen IV works for the original Diamond/Pearl/Platinum pokedex. Are pokemon like Glaceon, Tangrowth, Electivire, etc.. that received evolutions in Gen IV in diamond/pearl? What about new Pokemon like Rotom? Basically looking at this list at everything after manphy.