Perm doesn't include NIW and dependents. Perms data are for China and India only (EBROW won't wait this long). So it's hard to say that one year can clear all those PD. I hope so. When PD move faster, those old PDs will lose their desire to upgrade to EB1. It's a dynamic/balance thing, including perm/spillover, EB/FB, etc.
It is calculated based on the FLC data. After 2006, FLC only releases approval date in their PERM database. "2009 10 156" in the table above means 156 applicants were approved in Oct 2009. To better estimate the pending EB2/3C pool, we have to take the average processing time of 2 months (55 days in 2006) into consideration.