Here's more info from my "SCSW book".
17-6 1990 Full lug barrel with new yoke retention system. Some early 17-6’s reported without full lug. 1993 Discontinue 8-3⁄8" barrel.
17-7 1994 Drill and tap frame, change rear sight leaf, change extractor. 1996 Model 17-7 discontinued for Introduction of 10-shot Alloy Cylinder version Model
17-8 (see below). 17-8 1996 Introduce 10-shot with an Alloy cylinder 42 oz. 1996 Begin shipments in foam filled blue plastic case. 1997 Ship w/ Master trigger lock/ change to MIM trigger. 1998 A Change in frame design could have occurred here at this time. period, but no evidence exists to suggest that it did, other than the Heritage Series in 2001. 1999 Discontinued in late 1999. 17-8 2001 Model 17-8 Heritage Series- 6-shot-with CNC New Frame Design
17-9 2009 Model 17-9 available as Part of the Classic series introduction with internal lock, 6-shot cylinder with square butt frame, Patridge front sight with 6-inch barrel and wood grips.
Supica, Jim; Nahas, Richard. Standard Catalog of Smith & Wesson (Standard Catalog of Smith and Wesson) (p. 216). Gun Digest Media. Kindle Edition.