First came the roughs:
These sort of things reach me by a trickle-down effect. Contrary to common assumption traditionally published authors (at least at my level) have almost no say in their cover design. They might be asked for a selection of scenes the artist could consider, they might be asked for descriptions of the characters, but basically they're bystanders. Which means I can't take any of the credit for my covers, and that the fact that they are (in my opinion) excellent, is someone else's triumph and my good luck.
Each year Jason Chan provides the publishers with a number of sketches and they decide which one to take forward to a full cover.
These are the three I know about for The Wheel of Osheim.
The powers that be at Ace decided to go ahead with this one. Jason Chan polished it to a high shine (see the stages for King of Thorns), the art department at Ace worked on titles, quotes, and background, and presto:
Voyager are going to use the same artwork for the UK cover. Like Ace they'll send it to their art department to work on the lettering and background in order to ensure it fits in alongside the previous covers.