Anyone with a little common sense knows that the production and design of currency is very strict. How can there be typos or other patterns? What kind of collector are you? Coins are only a small part of the collection field. In my understanding, double mistakes are two typographical errors, and conjoined banknotes refer to coins that have not been cut and circulated before the issuance of banknotes. It is precious because there are few full-page coins, especially in the strict paper field of coins, typographical errors are even scarcer. As for the collection, the value is naturally high when the quantity is small, but in your society now, fakes are rampant. I think you should focus on it. The following is the information I found on the Internet for your reference.