June,
Thanks for your message. I saw the image relating to the marriage in 1820 and it certainly seems to me to say Platt. That is definitely mysterious, as the 1851 and 61 Censuses say Flatt. Are you absolutely certain that Richard Flatt who died in 1853 was married in 1820, to the sixteen-year-old Ann(e). I would have expected the marriage record to say "with the consent of parents" in that case, but perhaps they pretended to be older than they were. Do you think Henry b1825 is their first child? Might Ann be a different person from Ann Tate?
The Family Trees submitted by many people to Ancestry.com, which are often inaccurate, divide into two groups. Some have the Richard Flatt who died in 1853 married to Martha. This is Martha Pizzey, who married a Richard Flatt in Stepney in 1831. However, these trees are bogus as this Richard and Martha died in Marylebone in 1833 and 1837 respectively. The other half of the family trees do have Richard married to Ann Thornton Tate b1804. I think this Richard must be related to the Richard and Rebecca Flatt of Mundford. However there is no baptism recorded for Richard Flatt jnr in the Anglican records for Mundford. Maybe he was not baptised. Perhaps the family were Quaker, Baptist or other. Perhaps Richard is a nephew of Richard and Rebecca. I discovered that the modern name of Buckenham Parva is Buckenham Tofts. Anyway I will continue to search for clues and I know from searching for ancestors of my gtgfather John Nickols that they can be elusive!! Good wishes, Andrew