How can Official Game Guides be available for sale at game release dates?

I often search through amazon for new games. When doing this, i always wonder when i see a Official Game Guide book, which is available at release date of the game.

To write such a book, you will need to have a very early access to the game and information long before release date. So, I wonder, are these books written by the developers or someone at their company? Is this common behaviour to already write and produce a complete guide parallel to the development? Or is this done by a third party, and how to they get all the Information they need to write such a guide?

So, question is, who makes these guides, and how are they made?

An example would be the Fallout 4 Vault Dweller's Survival Guide which is available on 10th Nov; same day as the game release.

Every guide features in-depth content, detailed screen captures, quick-reference tips, and professional strategy

Hardcover: 448 pages

IMO, so many details can be not provided by only playing a beta or pre-release version...