I have updated my firmware several times over the years and documented the effects on WP numbering. My WPs up until April 2011 do not have the WP designation in front of them. They start with a 0 and are numbered sequentially. The WP designation only started with a more recent update (don't know which one) in 2011. When that update was installed, the WP numbers started all over again with the WP designation in front. So I have both 001 and WP001, which are different WPs.
At the time of the switch, the snapshot designation also started over and caused a lot of confusion. I have many duplicate S designated waypoints that need to be renamed since they are in fact different locations. For example I have 2 S00024, 2 S00023, etc. For some reason or other the duplicates started at S00020.