That must have been a huge amount of work.

Can I echo Jack Campin's point, about whether the names or first lines of any songs are known earlier from references in literature or as the names of tunes published without words? (I think that is the gist of what he said).

In that context do we know if, and if so how commonly, publishers modified the name of songs when appropriating them from elsewhere? I guess editors might pick a 'headline' that would sell.