Yes. The individual blood glucose reading is generally useless for long-term diagnosis, though you would be able to determine if someone were in hyper- or hypoglycemic shock and could then administer an appropriate palliative for the immediate condition. The only time this particular test is really useful is if you are taking a sugar sensitivity test where you take a sample, drink some sugary beverage, and take a few more samples to get a profile of the rise and fall of blood sugar over a period of a couple of hours. Otherwise, the A1C is the better diagnostic tool.
I should add that long-term trends in blood glucose CAN be useful when taken in consideration with other readings include blood lipids, so the test is not totally useless for diagnostic purposes. Just not so good by itself except in specific situations.