Around '91. I also have one that's BNBxxxx and when I called S&W they told me Nov.'92.
I also have a 60-7 which is identical to the 36-7 but stainless.
The -7s were the last .38Spl versions before they got chambered in .357MAG. They got wider front/rear sights, were factory heat treated for +P ammo, and were the last ones to still have all tool steel, not MIM, parts.