from 2009 to 2011 there were 5million coins mined, from january 2009 satoshi and other programmers (a small group) were all playing around with mining and making the first few versions of the bitcoinD
SATOSHI DID NOT OWN ALL MINED COINS OF 2009 as others were mining it too
2010 it started expanding where a few hundred to a couple thousand people were mining, meaning satoshis slice of the pie was getting smaller
in 2011 CPU farms and then GPU started growing, meaning that alot of average joes were getting a nice slice of th reward pie.
although satoshis hoard was large, if you do some actual maths of miners around between 2009 and 2011. satoshi did not have 20% control of all mining for the whole 2 years, which would result in a 1million hoard. id say he had 50% control at the first month of release, then dropped to 20% before summer 2009 and then dropping ever since, as bitcoin mining started to expand. id say he has about 100k not 1mill.
but no one can know for sure how much hoard he has, we can only speculate via the maths and putting known data into prospective... all i know for sure was that there were not just 5 miners in 2011 thus impossible for satoshi to have been at 1mill in 2011, when he disapeared
The first difficulty increase took place ~1 year after the genius block (dec 30 vs jan 3, both 2009). The difficulty is recalculated once very 2016 blocks and back then one block was worth 50 BTC.
50BTC * 2016 blocks means that
BTC100,800 is mined every two weeks. By following your assumption that he controlled 50% of all mining the first month it would mean that he would have mined ~100k the first month.
If he controlled 20% of the mining from February 2009 to December 2009 then he would have mined
BTC40,320 per month. This times 11 months is
BTC443,520 for this time period. Add this to the 100k from his first month of mining and he would have mined just under 550k
BTC assuming that he stopped mining when the difficulty first increased.