I have just solved a puzzle, but it raises a further question. I found index entries for the births of two of my step-cousins twice removed registered in Wales in 1995, but one in October and one in December. I have now ascertained that the birth of one was registered about two years earlier with his mother's surname, before their parents married. Does anyone know of a clue that I should have noticed indicating that an entry in the G.R.O. dataset refers to a re-registration? I expect that most of us know how they were shown in the paper indexes on which we practised weight-lifting.