The chances that anyone has ever shuffled a pack of cards in the same way twice in the history of the world are infinitesimally small, statistically speaking. The number of possible permutations of 52 cards is ‘52 factorial’ otherwise known as 52! or 52 shriek. This is 52 times 51 times 50 . . . all the way down to one. Here’s what that looks like: 80,658,175,170,943,878,571,660,636,856,403,766, 975,289,505,440,883,277,824,000,000,000,000.
To give you an idea of how many that is, here is how long it would take to go through every possible permutation of cards. If every star in our galaxy had a trillion planets, each with a trillion people living on them, and each of these people has a trillion packs of cards and somehow they manage to make unique shuffles 1,000 times per second, and they’d been doing that since the Big Bang, they’d only just now be starting to repeat shuffles.
I never really believed this - people shuffling cards don’t randomly pick each individual card - they make approximately 7 shuffles, each comprising 3 or 4 cuts without much variation in the size of blocks they choose.
This can be seen in any games which are particularly sensitive to seeing certain cards grouped together - the shuffle would have needed to actually made a cut between each pair of cards to ungroup them.
If anyone were to do an actual study of card shuffling, I think they would find a lot less entropy than 52!
You’re right, the argument relies on the shuffler actually doing a decent job, which merely overhand shuffling a couple of times falls laughably short of.