I don't know which guide you bought, or which page the "error" is on, but Bonsly and Mime Jr. are each in both games, but have opposite appearance rates.
I prefer Nintendo over Prima, because even while NP DOES make a mistake every now and then (often mixing up "right" and "left"), I still feel more comfortable with the official thing. Not to mention NP's guides are infinitely better organized, fitting more info into fewer pages, and are made so you can easily remember where to find something instantly. Prima doesn't do that for me.
One guide I sure hope they do well with is their
Ultimate National Pokédex: it's two guides in one! It's supposed to have ridiculous amounts of data on "all" 490 Pokémon, AND it acts as a walkthrough for Diamond & Pearl's post-Elite Four game. The BEST part is it's size: over 360 pages! (You ever seen the Kingdom Hearts II or Final Fantasy XII guides? Yeah. It's bigger than THOSE.)