Hi Erica,
Welcome to RootsChat!
I noticed (from the National Probate Calendar) that Harriet's full name was Harriet Emma. From this, I think I have found the marriage record of Thomas & Harriet.
Year: 1909
Location: Basford, Nottinghamshire
Harriet Emma SMITH m. Thomas WATSON
Here they are in the 1911 Census with their daughter, Evelyn:
https://www.familysearch.org/ark:/61903/1:1:XWSZ-4LB(If you do not have an account on FamilySearch I suggest you create one because it is free and very useful)
I think the confusion stems from the fact they actually lived in Nottinghamshire but moved to Derbyshire at a later date.
Could you give us the name of one of Thomas & Harriet's children (who is deceased as per RootsChat rules) as then we can search for their birth certificate and confirm their mother's maiden name is in fact Smith.
Queenie
