Nice, thanks for the info!

Well, you can have keys that mimic bundles just fine, even within the setup I described above; After all, each different key/package/bundle is its own license, and those still exist regardless of whether or not they're listed in the store. The problem is, SG pulls information via the API that is based on the information associated with store page listings (first, as that allows data to be dynamically updated and, second, because the API blocks certain information [such as ownership information] for unlisted games).

Any game that isn't listed on Steam (due to being an unlisted key or due to being pulled from the store) won't be able to be listed on SG without staff manually adding an imitation listing [ie, something they'd statically set all the information for locally]. Due to, among other factors, the difficulties of continuously maintaining an accurate listing manually, staff only does this for games they're certain won't be readded to the store. Thus, something that is in the store, even as a bundle, isn't something you'll see added to the list.

What's typically the case in these circumstances is that there was a key form released off of Steam and a Bundle on Steam. In that circumstance both would have different licenses, but provide the same content. (After all, given how special bundles are, it's understandable that developers can't use that same license for keys).

Though, given how old King Arthur is [ie, with the Collection possibly predating the addition of the <Bundle> configuration on Steam] it's possible it was released as a package first and then changed into Bundle format later on. So there is still a possibility that what you're describing was actually the case. But, either way, the fact that the license isn't listed in a non-Bundle format on a store page means that SG can't properly handle it.