Hi Brian,
A lineal descent can easily be traced between members of the Elfin Knight family albeit some of the links are quite scarce. I suppose it could be argued that 'Acre of Land' is a separate song because it only utilises half the original and has changed the purpose of the song completely. But with the 'St James Infirmary the odd isolated bits only make up a small part of the new song, almost commonplaces or motifs.

We have toyed with the idea of giving the various oikotypes of the 'Unfortunate Rake' family separate numbers or some sort of separate designation but it's not really feasible at the moment.

We have done this with the even more difficult and ancient 'Died for Love' family, i.e., given them separate numbers.