Hi Rob
Will try to help and add my two pennyworth!
You say;
Mary DAWE b. about 1793 in either Ermington or Harford married Samuel SMITH on 16 October 1812 in Harford
(on the marriage by banns both otp both made their mark witness James Elliot and Sarah Cove make their marks)
Mary died 1861 in Ugborough
(all in the Ivybridge area). These areas are well away from the Plymouth and Tavistock but many people migrated to Plymouth to work in the Dockyards.
For Dockyard workers try
Plymouth Dock Artificiers
http://genuki.cs.ncl.ac.uk/DEV/Plymouth/PlymouthArtificers/Or try a search at National Archives
http://discovery.nationalarchives.gov.uk/SearchUIIf Mary Jnr was the d of John Dawe do you have his baptism and where do you believe he was baptised? How is he linked to Mary Snr?
family 'legend' saying her mother was Elizabeth LEE
John Dawe married Elizabeth Lee 20 Dec 1810 Stoke Damerel, Plymouth. John Dawe was a Labourer in the Dockyard and Elizabeth a Spinster. They both signed, the witness were; Thomas LEE (her ?brother ?father) who signed and Wm Roberts who also signed other marriages on the page so perhaps a parish clerk.
On Mary Dawe’s 1840 marriage certificate her father was John a Labourer both were living 30 Fore Street. Stonehouse (Plymouth). Mary and William both made their mark. The witnesses witnessed most of the marriages so not family.
Where was Mary Russell in 1841?
John Dawe + Johanna Tarthewey, 24 Dec 1828, Stoke Damerel
John Dawe was a widower when he married Johanna Tarthewey he signed she made her mark. Witness John Bass Boon and John Lyne.
BUT looking at the signatures JD and who married Elizabeth LEE previously may have married Mary Hocking in 1807 in Plymouth. This JD was also a labourer in the Dockyard the signatures are very similar.
There are also two other marriages in Plymouth of JD to:
A Elizabeth Burgoyne in 1825 and to a Betty Sloggett in 1827. (no occupation or status given on certificate) These signatures look a bit more confident than the Lee and Hocking marriage but there other other JD’s also marrying in the area who could have been the widower who married Johanna. The originals are available on FindMyPast and need a bit of studying.
Hope this helps