Visa bulletin.
In order to file your I-485, the PD must be current. Accoring to various
sources, the cut-off date for EB2 China in October will be April, 2005.
You can only file I-485 when your PD is earlier or equal to that date.
Suppose your PD is April 19, 2007, you may check the visa butlletin to
find when the cut-off date becomes April 19, 2007 or later and then file.