I don't see why pinprick testing would help; it's not like a regular draw is that unpleasant (I went through a period of my life where I had two cylinders drawn every week).
The opposite problem exists with the tiny samples: blood like any other fluid, is not at all points identical at all times. You can easily demonstrate this for yourself: go to the drug store and buy a cheap glucose meter and take a bunch of samples just around the same finger, much less different fingers. You'll see a surprising level of variation. The larger samples of a conventional draw are shown to vary less.
They still vary (as the line you quote says) but less than the highly local samples.
The opposite problem exists with the tiny samples: blood like any other fluid, is not at all points identical at all times. You can easily demonstrate this for yourself: go to the drug store and buy a cheap glucose meter and take a bunch of samples just around the same finger, much less different fingers. You'll see a surprising level of variation. The larger samples of a conventional draw are shown to vary less.
They still vary (as the line you quote says) but less than the highly local samples.