The problem with most of these spreadsheets is for the later periods. For example, your spreadsheet assumes that the difficulty will increase by 265,669,181,621 on 13-Oct-2014. That means an increase in the network hash rate of 1.9017341e+18 h/s, that's 1,901,734.1 Th/s

I doubt that would be physically possibly even if every foundry on the planet was cranking out ASICs and there was enough labour and resources to assemble mining systems without any delay.