What is the total coin supply for grand coin?
From the OP, when everything is mined there is supposed to be a total of 1,420,609,614 coins. Some of those are likely lost over the years.
On the exchanges, what I can see on Cryptopia's book is about 62 million so far, so not much.
If we do the maths and if I do them correctly, it's roughly 800M :
1/ Block 1 to block 700,000 = 1000 GDC per block = 700 million GDC
2/ Block 700,001 to current block 897,000 = 197,000 x 500 = roughly 100 million GDC
But as said, who knows how many coins were lost forever on Cryptsy... I'd say a lot as it was the only exchange hosting GDC.
It should be interesting to see what makes its way back and to see what's being mined. You're working on the white paper?