How many Bitcoins existed when block 209,999 was mined? This article claims there are now 10,499,925 bitcoin (at the time of the reward drop from 50 to 25).

Weren't there supposed to be exactly 21,000,000 / 2 = 10,500,000 BTC mined at this point? What am I missing?
I suppose this is the culprit. If we add the duplicate 50BTC that is missing and the first reward from block 21,000,000, we would have 10,500,000BTC in total.

However, my calculations would be: 21000000 blocks (ranging from Genesis Block 0, to block 20,999,999) multiplied by 50 BTC, that would give us 10,500,000
With the duplicate transaction, that would be 10,499,950 BTC total.