I discovered today that you can build a ring kit on the Titan site that contains ring sizes that Titan doesn't actually sell. That doesn't work out well when someone buys the kit because the system doesn't put the unavailable ring sizes in the cart, doesn't put the unavailable ring sizes in the Wish List either, and there is no message provided to the user that a portion of the kit wasn't put into the cart. You just have to notice when reviewing your cart contents that something is missing.
I'm not talking about an "out of stock" situation here. For example, I constructed a kit that contained 2-3/4" rings. Did that because that's the ring size Capcom specifies for Breakshot slings. When constructing the kit the drop down for ring size does have an entry to select 2-3/4". But if you were to try and add a 2-3/4" ring directly to your cart you would find that there is no drop down for that ring size at that point.
Perhaps the ring size drop down list used in the kit construction needs to be the same as that used during direct ordering? Or, perhaps an error message should be displayed to the user when an item in a kit can't be added to the cart during purchase of a kit? Might be another way to handle it. The "kit" feature certainly is a nice feature to have from a customer standpoint.