I am fairly certain that if I had been tested I would have shown up as diabetic years ago - but I never was given a blood test for glucose levels.
I have been told that I have had annual health checks - but all I ever got was a blood test for the Thyroxine supplement being adequate, nothing else, and then no follow up as it was fine. I suspect that to some extent there are more diabetics being diagnosed because more people are being tested, not entirely down to more people developing the problem