Hi all,
Having looked through my headstamps, the latest D^C one I have is May '09. The next date I have is October '09, by which time it has changed to DA. It stayed as this until May 1910 (which was the last time they included the month in the headstamp) when it changed to DAC.

As others have said, this is either a poorly-struck headstamp, or a broken bunter. If it was clearly struck, I suppose there may be a very faint chance it might indicate some sort of special/experimental load (both RG and R^L over here sometimes ground bits off bunters to give odd headstamps for experimentals) but it is a very long shot.
Roger.