In the first of my examples the child had the same name (two christian names and a quite uncommon surname) on both references and of course same mother's maiden name. The parents had been living together and registered her in father's surname. So the later record had the same surname and coincided with when they married, So no change in surname in that case.
This is quite recent so there is no image as GRO index was computerised by then.
Also just found her sister, again two register entries, one actual year of birth and the second the same as the parents marriage year, her second register entry is consecutive with her sister's.