On "Dan Wesson Collectors Association" (website) is this information (in part) - clicking under "History".
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1969 - Model (or W) 11 (fixed sight) and Model (or W) 12 (adjustable sight).
Models 11/12 Series featured external barrel nut, and "porkchop" styled shrouds.

1971 - Recessed barrel nut debuted with 14/15 Series.
Models 14-1/15-1 incorporated new sights, extractor rod, cylinder latch, etc.

1975 - Models 14-2/15-2 Series of revolvers saw elimination of the footed "porkchop shroud" to "straight" shroud.

Also, the difference between Models 14-2 and 15-2 remained the 14-2 fixed sights as opposed to the 15-2 adjustable sights.
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I have a treasured Dan Wesson Model 15-2 (Monson Mfg.) and a Dan Wesson Model 44 (Monson Mfg.) Both sporting a deep blued finish and are drop-dead gorgeous.

Vintage Dan Wesson revolvers are getting harder to find out there and HAVE been developing a strong 'cult' following.