These are the first experimental coins made by Casascius. They were used to test the holograms to reveal the honeycomb pattern left behind, without ever being funded.
The coins can be identified by looking up the public key on a peeled, seemingly ‘pre-funded’ coin. If no BTC has ever been in the address, then it is possibly a demo coin. Currently, demo coins are only known to exist in brass 1 BTC form.
Casascius sold these coins to prior buyers as extras. On a few occasions, buyers who ordered Casascius coins
had the option to also buy some ‘demo’ coins along with them.
While no numbers relating to these coins exist, it is no doubt that they are extremely rare compared to the mintages of normal Casascius coins. It has been suggested that these coins may be an effective way to invest in the collectible value of Casascius coins without exposure to BTC price fluctuations.