Any 17 WSM that isn't loaded with 15gr, 20gr, or 25gr poly tipped bullets is old stock and has been discontinued some time ago.
I've talked to Winchester and all of the 20gr poly tipped ammo is loaded the same, regardless of what the label on the box says.
I have also taken a few of the 20gr tipped 17 WSM from, AE, Win and Hornady apart and weighed out the components separately. The bullets and powder charge in all of them, regardless of label, has pretty much been spot on with all of them and case weight was also nearly the same. Where the big variance comes from in the 17 WSM ammo is in the priming compound. Their QC on how they prime these cases, to put it mildly, is terrible. Some cases, even from the same box, will have substantially more priming compound than another. Some had the priming compound all down at the base of the case while others would have it slopped up the side walls of the case. I had some with as much as 7 tenths of a grain more priming compound in it than another. How much that affects velocity or anything else, I don't know and I could never get Winchester to give me an answer. The only answer they would give is, "this is production ammunition, not target grade". So with a response like that, I suppose we should be happy it's not worse and be greatful these things shoot as well as they do.