The april 1:1 btc snapshot was accessible through claiming for 6 months. Only 1.6 mil were claimed by btc holders of the 16.6 snapshoted amount, if I'm not mistaken. so there was about 15 mil coin still in the devs hands. Devs kept 10% of the unclaimed coins for marketing and such. Mining, trading  and airdrops started, and about 400-500k additional btx where put in circulation  Come november 1, claiming of the 1st btc snapshot was ended. A new btc 1:0,5 snapshot was taken on nov 2, and 8 mil btx was distibuted to corresponding btx addresses. No claiming necessary.
That puts the circulating supply to about 10 and a total of about 6.6 mil btx in the devs hands. 5.1 mil in #1 address and 1.5 mil in the dev fund. The remaing airdrops will be funded from the 5.1 mil in #1 aidrop address.
When the airdrops are done in next year, circulating supply will equal about 15.5 mil + 1.5 mil dev funds = 17 mil.
The remaining 4 mil from the 21 mil total cap will only be accessible through mining.

It's not rocket science people, I can't make it any simpler without having to draw pictures for you.
Anybody who doesn't  understand the concept by now, Will probably not be making a lot of money on this coin.

My 2 sats.

Full disclosure.
I'm not affiliated with the Bitcore dev team, in any way shape or form.
I just like to read up and do my research, before I invest.