Laws' system points out several problems in indexing folksongs. Firstly, it's hierarchical; if you want to assign a number to, say, Stagolee you have to decide whether it's a Ballad of Crime and Criminals, or a Murder Ballad or a Ballad of the Negroes.

More seriously, and this is a problem shared by every index I've encountered, deciding the number that should be assigned to a new entry requires you to at least roughly familiar with every other entry. A definition of the characteristics that define an entry would be very helpful, if it were provided; sadly, nobody--from Child to Roud--does this.Which leads to questions like "Is Billie Boy really a variant of Lord Randall"?