Hello Janet
I'll be down at the RO later today, and will look again at Marianne's baptism entry in Turkdean, also look at baptisms for later children of Robert & Anne, if any. The other ones I found were older than Marianne. It was not unknown for children to be taken back to the home town of one or both of their parents for baptism, so even if Marianne was born in London, she could have been brought "home" for baptism.
Not sure about Robert moving to London as part of his apprenticeship, but it's always a possibility. Maybe someone else can help on this.
Did you find Marianne on the 1851 census? And did this also give London as her place of birth? What about the 1841? If she was living in Southwark, this may have shown her as being born "out of County". Can anyone else help on this, please? I don't have Ancestry.
Unfortunately Marianne's marriage took place before the registers giving fuller details were brought in, so all you would see would be the names of both spouses, whether of the parish, whether by banns or licence, signatures or marks of the spouses and two witnesses and the vicar and date.
Don't believe everything you see on a death certificate!
The details are given by an informant, who may be relying on hearsay. For example, on the death cert of a New Zealand relative from the early 1900s, his mother's name is completely wrong. It's shown as a combination of his grandmother's first name and his mother's step-father's surname! (Caused us all kinds of trouble to sort that one out!) This is particularly evident with people who have emigrated and have no close family to verify the facts, so just rely on old memories.
I'll let you know later if I find anything.
Gillg