http://pokemondb.net/pokedex/blissey
It says it's base EXP Yield is 255, which is wrong according to Bulbapedia:
Blissey has the highest base experience yield out of any Pokémon, with 608. Before Generation V, this figure was 255 and tied for first with Happiny, Chansey, and Arceus.
This means it's base EXP yield is only accrurate for gen 4, which got me Mike thinking, could this be the case for all pages?