Pre-Split OS:
Q1 2010: 1,155,924,808
Q2 2010: 6,001,851,926 - 4,845,927,118 issued
Q3 2010: 11,358,962,494 - 5,357,110,568 issued
Average: 5,101,518,843/Q so project 16,460,481,337 for 2010 plus a couple billion for 2011 so I would guess that they were getting close to the 20B A/S which is what triggered the split.
You'd have to be looking at somewhere in the 160M-190M range post split.