wow....this is very interesting
Raghavsood,
just using the collectible.money website, it would appear there are 1170 in circulation with only 158 redeemed of which this is one. Is this correct?
Cas coins have some variance in how different trackers represent them, as the list of addresses provided by Casascius accounts for addresses falling into different strikes depending on whether or not he ran out of addresses for a given denomination from the pre-generated list.
For funded coins, it should be accurate.
For unfunded coins/bars, all addresses provided by Mike were loaded - however, it is likely that a high-but-unknown number of those addresses were never minted for many series as he stopped production, or items were sold as DIY.
This particular coin is
https://collectible.money/item/S2CASASCIUS-1-1AgFq8x1LS, which as per his address list makes it a 1/647 items in that private key batch, and 1/96 redeemed ones.
Note that the silver die itself was also used for a separate batch of 1170 funded coins, with a total listed address list of 9900 addresses in that series. However, the majority of those were likely not sold.
Perhaps MJ has more background on the provenance of this specific item.