No, you do not have to beat the Elite 4 to get the National Dex in Pokémon Diamond.
The National Pokedex is given to you once the Elite Four is defeated.
Get the National Pokedex by seeing every Pokemon in the Sinnoh Pokedex
To get the National Pokedex, beat the Elite Four.
yes
you need to beat the elite four and then get the national pokedex for Oak.
You can face them when ever you want you don't have to have the national pokedex you can still face them as long as you have the 8 badges.
You can get other fossils when you defeat the Elite Four and the Champion and receive the National Pokedex in Pokemon Diamond.
The credits roll after you beat the Elite Four. However, I would classify the game as being completed after you have seen all of the pokemon in the Sinnoh Pokedex and the National Pokedex.
nation pokedex
bebe gives you an eevee after you have the national pokedex and have beat the elite four
You have to obtain the national pokedex (beat elite 4 and go to the lab of prof.)
SPRITOMB you can see it in the elite four.Champion Cynthia has it.It is her first pokemon.