Prep is evolving tremendously so better use online info, In Book you may not get any info about new upgrades like flow Scheduling, and some new features just Demoed at TC 18. So pl follow Online Info.
As Deepak mentions, as the product is constantly evolving your best bet is to reference the online content for the most up to date info.
Some other links that may be of interest...
Hope this helps, if you have any further questions please let us know
[Program Manager - Tableau Community]