These sort of decks look really interesting, certainly not something I've ever come across in the UK. Unsurprising given how few casinos there are. I was wondering though, are these decks ones that have been used in the casinos, or spares when they changed design?
PS, the 'interesting fact' was really good, makes me wonder what other menial things are being done by inmates that you wouldn't expect!
OK, there are two kinds of casino decks - canceled and uncanceled.
The majority of casino decks circulating among the public are canceled - these are decks that have been used on the casino floor at a table and have been played with. Typically, a paper deck will be used for only a handful of hours - anywhere from one or two hours to perhaps a shift, but not longer. They're not used at poker tables much these days, where they've been replaced with plastic cards, but they still get much use at blackjack and baccarat tables. When they're "decommissioned", they're bundled off to the prison system, sorted, packed and canceled. Cancellation used to be a simple drilled hole off-center through the pack, but these days they take a marker and draw a line on all four sides of the deck, put it in the box and saw an entire corner off the pack, box and all.
There's a rare few that don't get canceled. Let's say "Casino A" have blue and green decks with the same design. They decide to replace the green decks with red ones. The day the casino stops using the greens, the entire remaining stock of green decks can be sold off without being canceled - they're no longer in use on the floor and can't be used by card cheats to swap out cards in their deck for cards in play on a gaming table. Since casinos don't change their colors or back designs very often, and will probably try to do so when they're low on the old color in the first place, uncanceled casino decks tend to be far less frequently found.
An example of this would be the "Brown Wynn" deck that Theory11 was selling in their early days of operation. It was felt by some cardists that the brown Wynn Casino deck, Logo style back (as opposed to "Signature style") had exceptional handling qualities and T11 managed to get possession of a fair amount of the uncanceled decks. Some people make the mistake of thinking that, because it was sold by T11, it's a "T11" deck, as in something they created, when in fact they were simply selling it, just like how they (and I think Ellusionist as well) were once selling David Blaine decks.