Hmm, interesting ... will have to check Non-Confs too just to be sure, then, hadn't considered that.
It's just struck me that the much-younger sister of the mother on the register also appears to have baptised her illegitimate child in both Anglican and Catholic churches, the same day, 20-odd years later. No idea why, and until now that has been the only Catholic involvement in that whole branch I've found so far. So there might be summat in it...