[Siegmund]

Yes, with only a million ways for two people to be dealt hands, the same preflop action has happened many times. With about 55 trillion complete heads-up deals (52!/43!2!2!3!) there are still a great many heads-up hands that have never been seen, but a regular heads-up player will run into ones that have been dealt before somewhere every month or two, and is likely to see a few hands twice over his own lifetime.