The game uses the OSM map data for three different purposes:
* generating missions
* routing
* map tiles
Generating map tiles is a pretty simple and straightforward process, also it is enough to generate a map tile only if requested. Map tiles of very common areas (such as for countries, many players play in). If you zoom into some rarely visited area in game (let's say somewhere in a small city in Brazil) and no one requested this map tile since last data update, then the map server has to generate the images first before they can be shown. Also this is an efficient thing and thus can be done regulary without any (negative) performance impact.
However for routing, the Routing-Server needs to have large large large amounts of data for the whole world. For map tiles, the information "this is a street of type x" is enough but for routing there are many further data required such as height restrictions, barriers etc.
That's why the routing server must precalculate all the data before it can calculate routes more or less efficiently. Sebastian (the original developer and former owner of the game) did such an update in 2016 and announced that it would take about 7 days (https://forum.leitstellenspiel…hread/8281-karten-update/). I do not know if any other update has been made since then.
However I do know that the OSRM (Open Streetmap Routing Machine) Version used in game is deprecated and some versions behind current version. That means in order to update all the routing data and do precalculations, the game team needs to update many things on their side to be compatible with the new version. I am not informed in the current state progress of this upgrade. I also expect the team to give this upgrade less priority in comparison to new features.
I do not know which data the game uses for generating missions but I expect this to be similar to the routing data.
=> There is difference between the map that is shown (which is pretty up-to-date with the OSM state) and the map data used to calculate vehicle routes (which may has received the last update in 2016).
Hope that answers your questions