An example of this, from one of my own games, did not happen the other night. It was a blitz game, and my opponent kindly went down the main line of the Traxler (no wimpy Bxf7+ thank you). He was even generous enough to grab my knight on move 9, a move that I remembered was supposed to be bad, but for reasons that escaped me. It turns out that it this opinion may not be accurate (in the computer age), but the line he did play was still god for me. That is, if I managed to find 13. ... Be6!! over the board. Turns out I did not, going for the obvious 13. ... Bh3+ which only lead to a perpetual.
Now I don't know whether this move had been found in analysis, but it certainly didn't turn up in my database. So if you ever get the position after move 12 on the board, you now know what to do!
Litchfield, Fred - Press, Shaun
ANU Spring Blitz, 23.09.2015