It would be nice if that would explain these events. It doesn't. I have one location where it just "knows" the wrong speed limit (it knows the correct one a road earlier and it always is displaying the wrong one on the other road) and when leaving my village (which is not signed with a speed limit sign) it sometimes thinks the limit is 30 (km/h) where it is in fact 80. And will then continue this for a mile until the next roundabout, even though there are side roads that would cancel a temporary speed limit.
I don't know what is more annoying. The fact that the second thing is random, or that there is no place to report such things.