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.