Not that it helps (sorry), but if you were going to send in the original German docs, then you didn't need a dating certificate. If you hadn't sent in the original German docs, I reckon that you would have got a 1976 plate.
The Germans probably operate like we do here in the UK, where the DVLA default position is to allocate a plate based on date of first registration. For example, Gr8auntiepat's little Ford Fiesta is actually a 2009 model, but it was sitting around in a new car lot somewhere for a couple of years before it was sold, so it is actually on a 2011 plate.
A lot of the time, the US imports are given a plate for the year before a model was introduced, because Yamaha manufactured the frame (which is date stamped) the year before it was actually used.