We should show near every revision how many votes the post had at the time of publishing that revision.
It can be interesting to see, for example, that, if a question had some features that led to gaining downvotes; later the author edited it, and added some other features. Now the post has many downvotes, but we do not know why it has gained them, whether because of the later-added features, or whether it had many downvotes before them already.