Why can the BIS not take +rank15 in to account until you have it?

Im a healer trying to look a week ahead at my gear once i have and extra 3 corruption resistance on my cloak why is this not available to sort on the bis section of the website (premium sub) ?
Why has the cloak section not been set up yet with the extra ranks of corruption resist?

When you are looking at the BiS gear, click on the cloak to bring up the list of back items. Use the down arrow to the left of the cloak to expand the options to edit it. Pick the rank that you want to consider for BiS. Then, click on that newly modified version of the cloak in the list to equip it and lock it in. Your BiS will now use that new rank, which takes into account the appropriate corruption resistance.

You can also adjust your corruption target up by 3, which will show you what gear would be suggested next week. Just don’t forget you changed it once you get the additional resistance!