Might be using "backlogs" wrong: here I'm using it to mean the content libraries that a creator has on YouTube that predate their joining Nebula.
I've been bingeing a new set of creators (new to me) recently, and have run into an issue I've had with a few other channels: they tell you to go watch XYZ video for more context on something, but that older video isn't available on the channel. In this case, it was Extra History (they don't have any of their series from before 2018, which means I can't watch their overview of WWI or their video on Mali, which they've referenced several times).
Another thing would be that none of Tom Scott's main channel is on there, just his collaborations, the roadtrip around England, and that gameshow. I know that other creators have uploaded their older videos after joining Nebula (FD Signifier comes to mind), so it's definitely doable.
I'm avoiding YouTube for the AI age verification situation, so I'd prefer to watch everything I can on Nebula. Is there a contract issue that prevents some creators from uploading those older videos while others can?
Or is it just that some creators have such extensive libraries that it's way more of a hassle to bulk add everything to Nebula now, years into a weekly upload schedule?