This isn't all that uncommon actually it's not the vss or anything like that, I've seen this on about half a dozen hud equiped cars where the hud reads correctly and the speedo is off. The way we fixed this was to take the cover off of the cluster, turn the car on and let the speedo sit at 15 mph, then with a set of skinny pliers hold the shaft going into the needle and push the needle back until it rests at 0.