As suggested, I'm sending a rqst for a ltr to S&W.
MEANTIME -- fresh information rc'vd from "other" sources" have suggested that the unique "TBD" is an agency s/n of the contracting agency (ala: the Cal Hwy Ptrl 'CHP' s/n gunsl) --AND/OR-- that it represents an interim "transition" model filling the s/n gap betw the Gen 2 and Gen 3 guns. (????) Any comments gratefullyaccepted.