SAIS is practically a non-issue on these, at least from two years of paying close attention to this forum. I recall seeing one user having issues in that time. When researching failure issues keep in mind a fraction as many 200s were produced as tundra/sequoia.
16+ had everything of 15 and earlier, but a much updated exterior and interior (front row seats are very different including the material), infotainment, LED headlamps, and the 8spd.
At some point you got the auto folding mirrors, power upper lift gate, soft open lower tailgate, more advanced radar cruise... i’m out of details.
IMO KDSS screws should not at all be a determining factor. If you are buying a rust bucket it matters.. but you shouldn’t buy a rust bucket.
Whatever you get, clean up the KDSS valve face and apply some LPS3 when you get it home. you won’t have rust problems there after that.