I just did it too with a Jap import with no documents (nightmare ). If you have all the German registration docs you wont need proof for the year of manufacture.
If the German docs show the age, which they should, you shouldnt really have any need for the certificate. Has it been registered in Germany for road use?? If so it will have a V5, like ours in the UK I assume???
I managed to get a letter from a local Honda dealer for free confirming the age of my MC21, so chance it with locals first before forking out £30 to Honda UK for a bit of paper!
_________________
NSR250R MC21 (NEARLY SOLD!!)
VFR400R NC30 (SOLD)
Santa, please bring me a NSR500 and a SP-2 next year. Pleeeeease....