is that possible that over 6 billion coins are mined?
You should read about duckNote->DarkNote->DigitalNote Libertarian economy.
You can read about here:
http://digitalnote.org/whitepaper.pdfFast explanation:
XDN distribution was made for real market use: to provide the main (~70-80%) of coin units supply in the very first year of fair proof-of-work mining. No premine or instamine here, announce was load and public.
Here is the XDN block rewards in the very first year with classic Bitcoin alike block reward halvings:
320 000 XDN 1st month June, 2014
160 000 XDN 2nd month
80 000 XDN 3nd month
40 000 XDN 4th month
20 000 XDN 5th month
10 000 XDN 6th month November, 2014
5 000 XDN 7th month
2 500 XDN 8th month
1250 XDN 9th month
625 XDN 10th month
312.5 XDN 11th month
156.25 XDN 12th month
150 XDN <-- Constant minimum base_reward for DigitalNote.
+ with DigitalNote XDN Quantum leap 2.0 there was a blockchain deposit release, now in core, will be available in wallets very soon.
Blockchain deposit: + ~1% annual interest rate (new XDN), but blockchain deposits are "locked" XDN, so the amount of "active" coin units on market, ready for transfers, will be lower with deposits.
Like if 1/2 of DigitalNote users will deposit about 3bln of XDN, active, ready for operations amount will be -3bln XDN. Here is one more factor of strong deflation.
PoA based on deposits will be implemented in future to make XDN network even more secure.
XDN supply is an example of free market Libertarian Economy, XDN was on exchanges since the very first month.
Mining and trading is a source of XDN for users more more that 1 year. Now + unique bank alike blockchain deposit feature.