We know that the maps/navigation on the 17" is Google maps while the navigation that works offline and is the database that supplies the data which is used to generate the turn-by-turn guide and imagery on the instrument cluster is Navigon (with their proprietary map data, stored in the car locally for offline use).
(If you look at this screenshot you can see that updating the maps is an action in the Tesla firmware, I interpret it as "download the newest version of the [Navigon] offline maps to the car")
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However, it seems that real time data from Google Traffic will occasionally re-route the path, only this time using a function that is available in the Navigon system (which has not been employed in the Tesla UI software): avoid a certain route/road/intersection/area.
Looking forward to Whaze which will be so much better than this quilt of a nav user experience as construed by the Tesla software engineers...