My gggrandfather's brother Charles, according to a respected book on Afrikaner families, was born on board while his widowed mother sailed back to the Cape after her husband's death. His death notice says "Born in New Zealand". The New Zealand BMD in 2009 listed three Laurie babies born in 1859: "Samuel Lawton" with the correct (well, nearly so) parents, and "Margaret' and "Samuel L.", both without parents but labelled "Auck.". No Charles, so the shipboard theory might be correct, but that would get us into even deeper waters.
Auckland is on the wrong island, so I formed the theory that the clerk who did the transcription was distracted and wrote the same name twice. The New Zealnd BMD service does you a hardcopy, which turned out to be just the computerized information printed nicely. They kindly checked the handwritten index books, where the baby was still Samuel, but said that the trial stops there: the registers form which the index books were compiled had been lost.
This year (i.e. 2016) I revisited the New Zealnd site and discovered that Samuel L. was gone and Margaret had parents. They clearly had discovered a better index book for Auckland than the one they used before. My theory no longer explained where the name Samuel Lawton came from, and I had to face the facts: the baby was christened under a different name to the one under which its birth was registered.
I mentioned the matter to a friend of mine in New Zealand, hoping that he might know where church records for Lyttelton in 1860 might be available. He is a keen yachtsman, and told me, just so that I might know what an intrepid gggrandmother I had, that in those days only sailing vessels visited New Zealand and they all travelled one way: eastwards. She could not have sailed back to the Cape via Australia. She had to go via London, where all her in-laws lived.
This insight removed some mental blocks, and I soon looked in the right places, which I previously had dismissed as impossible.