IANAL, but that's the only way the number can really be 'verified', and even then it's a bit suspect. AFAIK, Subaru did not match specb #'s with VIN's. Look a way back in this thread, there is a member who has (I think) a specb brought back from the dead, but in the process it lost it's number plate. As I recall, he contacted Subaru about it, and they were unable to help.
For the spec b's that have been on this forum since purchase, it may be a little easier due to this thread and it's predecessors.
SpecB.LGT - keep in mind, the low number does not make the car any more valuable then any of the higher numbers.
Also, I see #004 was loaned out to car and driver for a review. Did not see anything about #002 though.
http://www.caranddriver.com/reviews/2006-subaru-legacy-25gt-specb-short-take-road-test