Yes, a person can become a type 1 in the adult years. Search about
LADA and type 1.5. Very often it's difficult to diagnose because many doctors start out treating the patient as if he/she has type 2 but the meds for type 2 don't work. The blood sugar drops and spikes all over the place despite the meds. There are specific tests to determine how much insulin the pancreas puts out, if any. Insulin therapy is needed but it's difficult to get through the haywire period.