The educated, literate people probably wouldn’t bother to write down the exact details of a low class gambling game, when literacy is rare and scrolls/books are expensive.

Interesting enough, the Roman Emperor Claudius, who was an enthusiastic dicer, wrote a book on gaming/gambling. It's been lost to time, unfortunately.

Literacy is a funny question in regards to the Roman Empire, as is the price of scrolls/books. There's limited evidence that scrolls and books were actually cheaper in the Roman Empire than in the 15th century AD, just before and in-the-early-days-of moveable type, and that urban literacy was fairly widespread. The big problem is that the vast majority of ancient writing simply has not survived the ages.

I'm not well-informed about the dodecahedrons or the theories surrounding them, but I'm inclined to find your explanation, while interesting, probably a bit too complex. Especially considering that coins were often slightly irregular in shape, as the mass-produced neat, perfect circles that we're used to are a result of modern milled coinage