It was state-of-the-art for Winchester LE ammo in the last half of the 90's. It was most commonly seen with black Lublox coated bullets and brass cases, but the company would make special runs, if requested, typically packaged in plain white boxes with "Q" designations (instead of RA9SXT), and if requested they'd leave the black coating off the bullets and load them in nickel cases.
The next version, which still contained the SXT designation in the name, but a symbol code of RA9T, benefited from some revision. As I recall, a major revision was that they lowered the velocity window for expansion in response to the growing popularity of shorter barreled pistol used by LE for plainclothes & off-duty. Some changes in the jacket notching & petal cuts was involved.
The last revision still used the RA9T symbol code, but the SXT designation in the name (on the box end flap) has been replaced with the T-Series designation. I have some of this latest version, but I haven't personally witnessed any testing of it, yet. They've reportedly tweaked the jacket design to prevent the "petals" from over-expanding and rolling over and under the leading edge of the mushroomed lead core. The new design, when expanded as designed, looks rather like a starfish, with the jacket petals expanding outward, but not folding back and under.
This is picture shows a couple boxes of the SXT/RA9SXT and then the following SXT/RA9T. I don't think I've taken any pictures of the current T-Series/RA9T box yet. (I've used more of the 127gr +P+ SXT/RA9SXTP & then the SXT/RA9TA version, as those were issued loads for some time.)
After a while, you almost needed a scorecard to keep the SXT/T-Series variations straight.
What with having used that LE ammo line in 9, .40 & .45 ... and 2-3 variations of it across each caliber ... I still find myself grabbing a box of either an older or newer version at one time or another. It doesn't cost me any sleep, though.