I didn't have proper tests but found my insulin needs rose very slowly over the first 8 years after my diagnosis and then plateaued.
As nothing else changed in my life - I didn't put on weight, change my diet, exercise less, have more stress, ... - I assumed my body was producing less and less insulin itself until, eight years after diagnosis, my last Islets of Langerhan stopped their production and retired. Then, my honeymoon was over.