Man of Honour
I dunno how it works but the speed limit system in my parent's newer VWs seems pretty good at detecting the current speed limit - not sure how much it depends on a database but it doesn't seem easily fooled and so far hasn't struggled when speed limits have changed recently, etc.
There was one instance where a temporary 30 limit was in effect due to roadworks and someone had thought it amusing to change the 30 to an 80 - not sure if it just rejected the 80 as an invalid speed sign but it still picked up it was a 30 instead of former 40 or 50 limit.
Our mk7.5 GTI did a stellar job of picking up the variable limits on the M25