[reggoboy]

Thanks, all, for the tips.

@Zubersoft - Thanks for explaining. It sounds like your feature solves the problem of people not left-padding numbers in Song Titles with zeroes. Makes sense. But it doesn't sound like there's any way to sort by numbers without putting those digits on the left. 

@Geoff's idea provides an alternative to sort: search. More clumsy and time consuming than a quick visual scan of sorted tunes, but it does work. I tried using the Custom field. Don't forget to go into Song Title Formatting and displaying it, which can be handy:

%TITLE%  %CUSTOM%

And I have confirmed that the %CUSTOM% portion doesn't export when I Generate Song List, so that's good. 

I kind of wish I could use:

%TITLE%  [%CUSTOM%]

but then all the tunes with no Sinatra # still show the [], which is unfortunate. 

Still, this is better than what I had before, so thanks :-)