Thanks Colin.
An Ancestry tree (without sources, grrr) has Abraham Jeremie Decombe 1798-1852 (parents and many generations of ancestors named, hmmmm...) marrying in London
a) 25.12.1824 Martha Neale 1800-1827
b) 24.12.1827 Mary Coxhead 1800-1843 (our 1837 marriage witness)
c) 26.11.1844 Sarah Morrell ?-?, with whom he at last had sons, hence the family tree I suppose.
Agrees with your latest finding so i expect it's credible.
As to why Mary de C signed: I see the scenario as follows.
Sarah HW was orphaned in Marlborough at 18, without siblings (that we can find) - though many cousins etc no doubt. Inherits whatever the bakery's worth, as only child.
Abraham Dymock, Lambourn neighbour and good friend of her father, becomes guardian, officially or informal.
SHW moves to London for work as housekeeper or companion - something a bit middle-class, as
a) she had inherited, though perhaps not much
b) she married a distinctly promising Bedford merchant, who I suspect wouldn't have married a servant.
By 1837 she's a good friend or in household of Mary de C, about 9 years older than SHW: who comes to the wedding because SHW has no close family in Marlborough and none at all in London, and signs register.
The Clerkenwell register does have a number of signatures x4 or even more, so perhaps it was the vicar's quirk to encourage extra people to sign, particularly for an orphan.
Does that work for you?
There are a couple of feasible Mary Coxheads born 1801 (none 1800 that I noticed) who are not ruled out by being elsewhere in 1841 or alive after 1843, but it's probably not something that needs pursuing.
Mike
