For the OP to make one's own decision, here are descriptions of the -3, -4, & -5 changes, whether they make a difference to the OP or not:
64-3 1977 Change to put the gas ring from the yoke to the cylinder on Heavy Barrel Versions.
1982 Delete pinned barrels
64-4 1988 New yoke retention system/radius stud package/ hammer nose bushing/ floating hand/ on 2" tapered barrel version
64-5
1988 New yoke retention system on heavy barrel 3" and 4"/ hammer nose bushing/ floating hand
1991 3" heavy barrel became standard production
1994 Change star extractor, change to synthetic grips
1995-96 Delete Square butt Features, MANUFACTURED. round butt only
1996 Begin shipments in blue plastic cases. Begin serrated backstrap and forestrap on a round butt frame for about 18 months, then discontinued
1997 Change thumbpiece/ ship with Master trigger lock/ change to MIM trigger
Supica, Jim; Nahas, Richard. Standard Catalog of Smith & Wesson (Standard Catalog of Smith and Wesson) (p. 264). Gun Digest Media. Kindle Edition.