DR Meant reportable to TOPs, not that I ever recall it happening as an op. that said movements were probably recorded at the operating base for hours, mileage etc for maintenance purposes.
DX was not reportable although few machines were as I recall, I think the GP TRAMM's were DX at first as was some of the last small machines (VDM800U which was at Taunton then Plymouth)
Later when I had access to tops for a while was never able to find OTP on the system.