Take away all the external factors such as contamination and, most likely, meter inaccuracy, and everything else being equal, I assume it is normal to have differing results.
I am talking through the top of my hat here and am probably quite wrong, but our blood flows quickly, so even in the short time between stabs there is completely different blood in the same place, and presumably not all our blood cells will take up glucose simultaneously, so 2 adjacent blood cells will have different amounts of glucose attached to them.
If I have a test that is outside my normal range I do another, and if that is wildly different, another. If 2 are similar, I take the higher. Otherwise, I average all 3.