Ah, OK, now I see the 50 you mentioned in the actual S4440 section of the Ref.
S-4440 Special distributor model. Only one variety of this model was made. Known s/n range 87-00010 to 87-01219. A total of 1,198 were shipped to Jerry's Sport Center (PA) from 1990 to 1991. Original retail $395.25. Note: Apparently, the factory ran out of .44-40 cylinders for the remaining cylinder frames (which already had the two-line "RUGER .44 CAL. CONVERTIBLE NEW MODEL BLACKHAWK" rollmark on them), so as many as 50 cylinder frames were assembled with normal .44 Magnum cylinders and then shipped out as the model S47N (two known, s/n's 87-01231 and 87-01245, see the chapter on New Model Super Blackhawks). Note that after the S4440 series was produced, Ruger began serial numbering again at s/n 87-02000 (s/n example 87-02109 – KS458N).