I personally scrutinize the idea that Sony sold over 160M PS2 consoles. The last shipped number was 155M in 2012, and they stopped manufacturing in 2013. It doesn't make sense to me for Sony to manufacture and distribute 5M+ extra PS2 consoles when they only shipped about 2M PS2's between 2011 and 2012.
Instead, I could see maybe 3M-4M additional units, 2M per fiscal year. In addition, Jim Ryans statement of 160M sold very much sounds like an unofficial number and could easily be a rounded number based on how close it was. 158M-159M is IMO close enough to 1) be a reasonable amount above what Sony last reported based on the shipping trends leading into 2012 and 2) close enough to 160 for Jim Ryan to adhere to that number through rounding. Especially if it's, say, 159.5M.
161M, as suggested for the upper limit, just seems too suspicious. I just couldn't see Sony deciding to manufacture 2M more units FY 2013 and then another 4M before they cut manufacturing.