When I last spoke to Tony his idea was that the song titles and their first lines would be entered onto an Excel spreadsheet and sorted alphabetically. This way it would be easy to see what had been already sung.
Distinct variants would be allowed, thus songs like "The New York Trader" & "William Glenn" would be allowed, because, even though they share some verses and tell basically the same story, the tune is radically different. "Barbara Allen", "Barbary Allen" would be allowed if distinct variants,i.e. not just different by one word, (once you've sung 'em its too late anyway)
Mary, if stuck you could always sing it in Welsh, no one in Essex would know.
Strangely enough the rules imposed on this sort of thing by the Guinness Book of Records do allow for repeats after so many hours, Tony wanted to see if we could set a new record without.