S&W eliminated the barrel pin from J, K, and N frame revolvers in 1982, and all centerfire Magnum revolvers had the cylinder counterbore eliminated at the same time. S&W collectors refer to pre-1982 Magnums as "Pinned & Recessed" or P&R. The K and N frame Magnums all got a new dash number when this occurred. For K frames, the first non-P&R .357Mag models were the M13-3, M19-5, M65-5, and M66-2. For all .357Mag N frames, the first non-P&R model was the -3.
Keep in mind that the pinned barrel and recessed cylinder don't make any measurable difference in how the gun shoots. It's mainly a collecting thing. P&R guns command higher values because they're older and more traditional, and many S&W collectors obsess about tradition.
The L frames were introduced in 1981 and had non-pinned barrels and non-recessed cylinders from the start. There is no such thing as a P&R L frame.
J frame Magnums were never P&R because the J frame was not available in .357Mag until the 1996 frame stretch.
FWIW pre-1982 K & N frames in non-Magnum centerfire calibers (.38Spl, .44Spl, .45ACP, etc.) never had recessed cylinders. OTOH all post-1935 rimfire Smiths, including today's production, have recessed cylinders to prevent case-head separations with soft rimfire brass.