A cheap answer would be for Youtube to present a last edited date for any video in an easy to check place. Since current copyright makes it difficult to make a

A cheap answer would be for Youtube to present a last edited date for any video in an easy to check place. Since current copyright makes it difficult to make a copy of the video and link to the copy, we've fallen into the bad habit of linking to things and hoping they don't change. Copyright interpretation isn't going to change anytime soon, and keeping immutable copies on Youtube might be too expensive. I say might, because, in the grand scheme of things, edited videos might be few. A last changed date would be enough for most purposes.