I noticed that listing only goes up through 2006, so here's some additional information that will help to ID the year going forward:
Some time during 2008
PRS started using a "08" instead of an "8" on the serial numbers.
For example, I just got in my first PRS in about 4 years - a KL1812. It has the "08" on the serial number (although it didn't leave the factory until early January 2009).
In looking at some guitars on a few websites I've found 2008s with both the "8" and the "08", so I don't know when they made the change; all 2009s have the "09".