Becky, I've had trouble retrieving the older threads myself. But so far I've had good luck by searching on the simplest things in the titles... for instance "Alphabet" with the letter I was looking for; plus I was finally able to retrieve the F's by searching on "Show Us F's"... But it does seem really hard, especially when I finally dredge one up and the title reads exactly as it should, but it simply didn't work when I typed it.
But the good news is... there are only 26!