Calculating Surface sales

http://blog.adduplex.com/2012/12/adduplex-windows-8rt-device-stats.htmlThe above link contains data from the AdDuplex network regarding the shares of different Windows 8/ RT devices as on Dec 7th 2012. Microsoft had said that it had sold 40 million licenses as of Nov 26th. It was a rate of around 1.25 million licenses per day. Let's take a rate of 1 million licenses per day for easier calculations(being conservative here). That's another 11 million licenses sold till Dec 7th i.e. a total of 51 million licenses sold. Assume the common argument that many of these licenses are still sitting on retail shelves. Let's assume 60% are such licenses (again conservative estimate). Thus we can infer that about 20 million PCs/devices are running Windows 8 and are being used as of Dec 7th. Now the AdDuplex data shows that around 6% is the market share of Surface i.e. 6% of 20 million = ~1.2 million. Now that 6% may have been rounded off from 5.7% too, considering all other devices are at a minimum of 1% and no decimals are being used. Thus, we can say that the actual number of Surfaces sold is a little lesser than 1.2 million. But, it is also possible that AdDuplex is unable to measure all the actual Surfaces in use (this can happen if that Surface does not use any of the apps on the AdDuplex network), thus we can increase the number calculated. All in all, this leads us to a conclusion that even conservatively >1 million Surfaces have been sold already. Does this seem a logical calculation?