I have a Taurus PT 99AF (9mm) with the nickle plated slide, adjustable rear sites and shinny aluminum frame, but no decocker. I've had it for probably 15 + years. I purchased it used from a gun shop. I recently tried the Taurus web site to enter the serial # to find the age, and don't think the info was correct; it said it was a 1995 model, but mine does not have the decocker, which I read started in the early 1990s. I found another source while searching for info on the age on my PT99 and based on the first letter in the S# (L) it is a 1992 model. Again, mine does not have the decocker, and I read that feature came out in the early 1990s. So, the info about the "L" being a 1992 model may be correct; perhaps it was built just before they added the decocker. I could have called Taurus and asked, but it was not that big of a deal.
Anyway, I wish I could be more help, but my PT99 is one of my favorite handguns and it shoots very well and is accurate.