It is difficult to be sure that the 1792 marriage shown is the correct one. I have found no other marriage of a John Richmond to a Susan or Susanna(h) that seems plausible. The name Johnson has been used as a second forename for some of her descendants. As a mariner, John would have travelled widely so his business could easily have taken him to St Marylebone.

The 1851 census shows her as being born in Kaston or Haston, Lincolnshire but no such places exist. I have looked at parish registers for many Lincolnshire parishes including those with a name resembling Kaston or Haston but without success. It appears that Keyston in Huntingdonshire or Cambridgeshire (I think the boundaries changed at some point) is about 20 miles from Lincolnshire and was once known as Kaston-on-the-Hill. Kaston may be Caistor but for most baptisms of a Susanna Johnson in the area there is a marriage for her recorded nearby.

Because marriage registers for Burnham from 1754 to 1774 seem to be lost (even Essex Record Office doesn't have a copy) it is possible that the marriage took place in Burnham (probably to a Susanna Johnson). It might even have been the Susanna Johnson baptised at Black Notley (Essex) in 1773 whose mother's maiden name was Richmond (if I have the right marriage)!