This is an interesting one!
The plate does look aged as in from '69 (ie the anodized finished has faded to a brownish colour as they do), and I had guessed it had been off for frame re-paint. NOS replacement rivets are available, but do come bright rather than brass finish.
KP's comment about 12/69 suiting a 1016xxx is spot on in terms of what we would usually expect to see, but the French 1014xxx sandcast should have taught us never to say never! The comment about it being held over for re-work in the factory seems to hold water?
Interesting comment (for me) was also the reference to it being a right side horn frame, definitely not the norm at that VIN.
Seems it is another of those fascinating examples that keep turning up. Look forward to seeing the frame / engine stampings.
Cheers - Chris R.