The dash stuff is a change history or Revision history. In the case of the S&W Model 586:
Model 586 Variants
586, 1981 Intro
586-1, 1986 Radius stud package, floating hand.
586-2, 1987 Change hammer nose and associated parts.
586-M, 1987 Product warning by S&W, M overstamp to indicate factory mod (for 586 and 586-1)
586-3, 1988 New yoke retention system. 1992 Delete 8 3/8" barrel and four-position front site. 1992 Delete nickel finish
586-4 1994 Drill and tap, synthetic grips, change rear sight and extractor. 1995 Delete square butt. 1997 Delete 8 3/8" barrel, change to MIM thumb piece.
586-5, 1998 Change design to eliminate cylider stop stud. Change to MIM hammer with floating firing pin, change to MIM trigger, change internal lockworks.
586-7, 2006 Limited Edition. 7-shot variant only.
586-8, 2012 Reintroduced under Smith & Wesson's Classic lineup. 6-shot only.
The Model 586 is about the same gun as the Model 686 but the 686 being stainless and the 586 being blued steel. Mine is a 586 no dash and I believe around maybe 1985 manufacture with the inside of the grips stamped Nov 1985. Mine is a 6" barrel.
Actually the 586 guns are relatively new making the original grips easier to find. Overall as how the revolver stacks up against some of my others? I see it as one of my more enjoyable shooters, actually I enjoy shooting it as much as my Model 19.
Ron