Just bought a Model 17-6 with 3Ts in 99% condition made in late 1988.. No box or docs but near perfect. I thought the 17-6 had a full lug bbl. but mine has regular non lugged bbl. When did they make the change to FL.
S&W started the full lug in about 1990. Keep in mind, they never threw any serviceable part out so there is a transition period which is where your pistol sits within. There is a notation in the Standard Catalog that mentions that some early 17-6's have been observed without full lug barrels.