Good point, Brian (01 Sep 14 - 02:49 PM). If a song that once was in vogue is sung later only by the same generation, it may count as nostalgia rather than true popularity.

I remember "You Are My Sunshine", first published in 1939, sung in 2005 by middle-aged pub singers in England. Of course, I do not know whether this is statistically representative, hence my question in this thread. As for "Yesterday" (1965), it is today sung by teenagers, e.g. in Germany, where I currently live. Typical question: "Grishka, what is the second chord of Yesterday in D major?"

Crib sheets are not necessarily an indicator of lack of popularity. I think they always accompanied folk singing, since the advent of literacy. Often we read that a folk song cannot be reconstructed in its original state because it had never be written down - chances are that many crib sheets existed, but none survived. Singing for pleasure need not be atoned for by avoidable exercises of memory.

The same applies to song books, as I wrote, unless they are treated as hymnals of the Folk Faith. (The relation between faith or patriotism and pleasure is a complex one, often sharply differing with culture and tradition.)