I have recently refurbished a pre-war Diana 27. The Diana name and the Huntress symbol is just about visible on the action. The barrel has Diana Luft Gewehr stamped on top and Made in Germany stamped underneath. But on the underside of the breech I found 11.28 stamped in small numbers. I am assuming this means it was made in November 1928. I have another marked 6.26 which I assume is June 1926. But I have also seen rifles with no 'date stamp' marking at all.
Cheers, Phil