Dude I think I ll just wait for a more official answer..
You denying things I have stated as facts wont get us anywhere.
Once again I did not buy a random skin.
From the champ select, (this page f.e http://i.imgur.com/maS1Ovb.png) with my player being thresh I clicked on a skin (i cant remeber which one, and cant remember if I saw championship thresh there),
That click led me to this kind of page http://i58.tinypic.com/mhqb8w.png where I navigated through skins.
In that caroussel Championship Thresh and SSW Thresh WERE there and available (It was Sunday, worlds were on, those skins are available).
I clicked on one championship thresh and bought it for 975 RP. Clicking ok on that window leads you back to champ select.
In champ select, having bought the skin, it was not in the available ones (it didnt show in picture 1 skins carousel)
This is exactly what happened and that's why I am posting here.
I own the skin, I checked it in custom game, but it was not there after the purchase in champ select.
Do you get it? I cant be more specific than this.