Appears you can actually search your youtube watch history here, I've always been annoyed that you can't inside the actual youtube website when I'm trying to find things I watched a few months earlier.
It's weird youtube can't even remember what I've watched. I'm constantly having to go into my recommendations and selecting Not Interested -> Tell us why -> I've seen this video before.
I think YouTube recommends those videos to you, because people are actually more likely to rewatch videos they have enjoyed in the past. So YouTube gets more views from old videos -> more revenue.