I always 'balk' at this idea because as we all know, the probability of two patients having the same blood type is high. We have had a few instances over the past few years where a wrong patient was drawn (we use BB Bands so it's very obvious) and they were the same blood type but one had antibodies and the other didn't.
And yes, there are those who have had to come up with 'defensive measures' to 'assure' that there is no 'cheating', e.g. RN draws 2 samples and holds one in case the BB asks for a second, a witness (do you really think that happens as intended?), different colored tubes for the second draw (assuming they don't draw the wrong patient twice).
I could go on and on about this ... but that wasn't your question, was it?