Is it possible to have diabetes (type 1 or 2) for about 9 months without knowing it ?
People with type 2 diabetes often have no symptoms at first. They may not have symptoms for many years.
Mild asymptomatic hyperglycemia precedes by months or years overt insulin dependence among persons with islet auto-antibodies.
In diabetes type 1, symptoms usually develop much quicker, though.
In type 1 diabetes, the signs and symptoms can develop very quickly, and can develop significantly over the course of weeks or even days - particularly in children or adolescents.
Speaking for type 1 diabetes, and supposing that a patient has exited his/her "Honeymoon" phase, the timespan before accusing severe symptoms (hypo/hyperglycemia) is very short and highly depending on what it is being eaten and on the physical activity done.
There are several indicators that could raise red flags, like: drinking a high amount of water (5-6 to 9-10 litres per day) with the consequent high frequency of urinating (a symptom of hyperglycemia), the need of eating voraciously and with more quantities (a symptom of hypoglycemia), and so on.
The fastest way to detect whether or not these symptoms are related to diabetes is with a simple finger stick blood sugar test.