Songbooks are a bit like woodpiles. They keep the songs ready until someone is able to bring them alive by using them to make a fire, when there's no wood lying around to be gathered.

The important thing to remember is that the song as printed is just a note of a single variant, or a cobbled together version made up of of different variants. The same goes for recordings. And the same goes for singers. The song itself is something broader than any of these.