Hi, Steve-
I think that's what's makes me uneasy, the connection between "Early, Early in the Spring" and "The Trail to Mexico." Yes, they're related, but can you really say they're the same song? I think that's a flaw in both Roud and the Traditional Ballad Index - there's no accommodation for songs that are somewhat related, but that need to be classed as a separate song. Both indexes seem to have an "all or nothing at all" policy.

-Joe-