One suggestion upthread was that videos that start public or unlisted can be made private without changing the ID. I haven't verified this myself, but if true

One suggestion upthread was that videos that start public or unlisted can be made private without changing the ID. I haven't verified this myself, but if true it could be a way to get around someone sharing a video, then making it private to hide the contents. Obviously this is less severe than if, say, all private video IDs were well known, or a one-up integer, but it's still a leak and could be exploited in real-world scenarios.