Possibly, but there would need to be a stimulus (publicity drive, national screening campaign, diabetic Big Brother housemate) for those to get diagnosed to get a more accurate picture.  AFAIK the publicity surrounding Jade Goody's Cervical Cancer prompted many young women to be tested, and thus some cancers were detected early, raising the actual prevalence rate. I don't think this had any bearing by spiking the estimate of undiagnosed cases.