The A1c is the ultimate judge and jury. It cannot be faked. A diabetic can fudge the numbers on the meter for his doctor, but the A1c tells the true story, every time. It cannot be fooled.
There are some exceptions that can affect the A1c, that the doctor will understand: a virus or other infection will often run a diabetic's blood sugar through the roof, so that can affect the readings. Also, taking prednisone can cause elevated blood sugar in some people, so that's another reason for an elevated A1c. A diabetic can have good numbers 90 percent of the time, but a week on prednisone or a round with a cold or flu can cause the A1c results to be a little skewed.
So, unless you've been ill or on steroids, your A1c will tattle on you every time if you've been naughty.