Avengenator and Hippohead are both correct, and that is the same technique I've used for RF releases. With all the successful purchases I've made, there has never been an instance where I DIDN'T encounter the "Inventory Issues" page. All you have to do is go back, and continuously try to check out again and again.
Kith's web developer, Andy, even wrote a blog post explaining how the Kith online store works:
http://www.kithnyc.com/2012/10/kiths-online-store-explained/.
In the blog post, Andy basically states that a size is not officially sold out until it is removed from the drop-down list on the product page. Therefore, for future reference, even if you guys encounter the "Inventory Issues" page, you should keep trying as there is a chance that the size is still in stock. All the times I've been successful with RF releases, I've always ended up checking out 20 - 30 minutes after the drop. Just got to have enough patience to keep trying to check out.