This isn't true. The genesis block references a Times headline published on Jan 3rd 2009, so that block was created no earlier than that. The source code was published and publicly available on Jan 9th 2009, which is 6 days later. Blocks were mined much slower than the target of every 10 minutes in the beginning. Block number 17 was mined on Jan 10th 2009. At 50 bitcoins per block we are talking at most 850 bitcoin or so mined "in private" before launching bitcoin.