Here is some info about the 5 BTC BitBill.
I cannot verify the initial count of 144, but let's assume it's close.
This figure was provided by Charlie Lee himself back in a much older forum post when he sold off his collection of Casc and BitBills. I failed to properly quote it in my prior auctions. But, it's safe to assume he would have used blockchain transactions to figure it out.
https://bitcointalk.org/index.php?topic=199785.0I also figured out how rare BitBills are:
20BTC: 181 (132 intact)
10BTC: 143 (97 intact)
5BTC: 144 (107 intact)
1BTC: 589 (492 intact)
This 1 transaction starting from an even 1000 BTC funded most or all of the 5 BTC bitbills. Perhaps a 1st or 2nd smaller batch is out there too.
https://blockexplorer.com/tx/9f9c271886e860898ca3781b21e20b734fda44c2c5e712bb936da61ca56bfe91As of May 1, 2018, there are 50 Unspent, and 76 spent outputs. The total count of 5 BTC outputs is 126 on the above transaction, which is pretty close to the 144 presumed in existence.
From this then it's safe to assume that there are probably at least 50 left intact, and probably not more than 68 of the 144 presumed to exist.