Yes, with multiple verses the version comparing all LyricText grobs didn't work, but the original one David had posted comparing the NoteColumns did work.
I need to get the lines to always be in the same place now horizontally, in case there are two in the same NoteColumn. If anyone wants to tackle that, such that the horizontal line it adds below the syllable will be relative to the horizontal position of the note, rather than of the syllable, I would be grateful, but I suspect I will be able to get it eventually myself, I simply constantly refer to the documentation.
It may also be that the fellow I am working with wants the first syllables all to line up on the left, with only the longest centered beneath the note, as in the forum thread that Kieren had referenced earlier. If this is the case, the markup code works as is, and it is the X-offsets of the syllables themselves that will need to change, so I will have to find that out before I start playing more around with this code.
Again, thanks very much.
Benjamin Bloomfield