"The A1C test gives you a picture of your average blood glucose (blood sugar) control for the past 2 to 3 months. "
Ron
So I have been led to believe. That is, over the last three months, with the most recent month being the most influential. It just so happens that cost and inconvenience of quarterly testing more or less dictates semi annual testing instead of quarterly.
The high readings that some experience are called "the dawn effect". On theory is that with a normal metabolism, blood sugars fall after the spike caused by eating and the little liver dumps glycogen to make up for it. At this point, with a normal metabolism the pancreas releases enough insulin to keep us in the normal range. Normal metabolism is not what you associate with diabetes.