Unarchived karaoke streams are ones which won’t be available officially on their channel once the stream ends. Going based off of this post, which says:
Any other music or music-adjacent video for stream, digitally, in a video site like YouTube, by a fan: YouTube also has plenty of videos such as fan recordings of live shows. These are music that often is not available in any other way, and it can be debatable whether they are live bootlegs, just standalone recordings, or something else.
I understood this to mean that these unarchived karaoke streams are allowed, so long as there’s a recording available at all. I’d assume if there’s no possible way to see the stream, that it wouldn’t be added, but I’m strictly referring to streams which have either an official or unofficial archived version available; for most of Hololive, its not hard to find such archived versions online, albeit often not on YouTube.
I could be wrong though, in which case pretend my post is only referring to the officially-archived streams, since this post isn’t really about unarchived streams being allowed or not.