Ho, ho!
Thanks for linking to that old post. I'd forgotten all about that.
I can see from the snippet showing the contents of the taxa_taxon_lists table that the child list refers to the same entries in the taxa table as the parent list so updates to the parent taxa will also update the child list. This means that child lists of the UK Master List will automatically be kept up to date with changes in nomenclature and NBN Taxon Version Key which is probably pretty useful.
The issue in that previous post was just to do with a report query that needed updating to take account of child lists. This could just have been an outcome of a report being used in a way not originally envisaged.
Jim Bacon.