You need to show pics of your barrel.
There are a few other possibilities other than it was just missed on the stamping. As I posted on the CMPicon forum, they stopped using both the W and the WP proof and used either just the W or the WP later in production. If you are a Carbine Club member you can read about this in the 6&7 million SN WRA update written by BQ97 from here on this forum.
Accidents happened is the markings of carbines see the post a few below here about the no name carbine.
Dave