Hi JER,
I think you may have misinterpreted Sue's point. The HBA1C will not tell you where any spikes are occurring, but it is a valuable indicator - it can show that you are having spikes that you are not aware of. If your tests show that your BS is consistently around 6mmol but the HBA1C covering the same period shows 7%, then that shows that you are getting spikes during times that you are not aware of and that, as you suggest, further tests at different times may be needed. This can be particularly true for type-2s, where over-production of glucose by the liver is very common.