I find TED talks are really hard to find, if you don't remember its exact title and/or speaker. The difficulty is that often you remember the basic idea, but not the keywords (since it might not be in a field you necessarily study).
So for example, you could think "Oh that one with the headband where they controlled the computer by thinking about it", but not know to search for BCI, or Brain-Computer Interfacing, if that's not your field. Searching for "controlling computer with thoughts" probably isn't going to get you anywhere either.
Besides that, I don't think their tags are all that comprehensive.
Recently in another topic I mentioned the "two bishops against two knights" chess endgame problem. I claimed it was investigated over two decades ago by a computer program and established that it is a win situation for the two bishops' side. Then I was unable to Google a solid reference for my claim.
I also remember a "Hermes Set Theory". It was something like ZFC, regarded as a valid Set Theory axiom system for 40 years, until a paradox was found inside. Now, I can't Google it out.
And then it was the so called "Baryon number conservation law", which was postulated for a short while in physics. Until it was found that a subatomic decay may in fact in/decrease the number of baryons in the process. I can't Google that one either.
Is that just me, or what?