Pokemon Platinum post-Elite 4

I downloaded the pokemon platinum rom, but now that I'm nearing the end I remembered that after you beat the elite 4 you can't get to any of the other good stuff like the national pokedex and whatnot in the previous pokemon roms.
So if anyone has a way to get to the extra parts on an emulator and rom, then do share info! ^^
BTW, using no$gba. thanks.

I don't think that it's true. I already beat the Elite Fours and i've already gotten the national dex and other legendaries. I also used no$gba.
Check if you are using the latest version which is 2.6a

do you just save before you beat them and then play the game when the opening scene comes out?