"She was listed as Polly Trewern Richards on her birth registration"
Not according to the index.
http://www.freebmd.org.uk/cgi/search.plBirths Dec 1885
TREWERN Polly Richards Penzance 5c/251
or her birth certificate ...her GIVEN names Polly Richards with mother Minnie TREWERN dau of Henry TREWERN, farm labourer.
You have misintrepreted the birth certificate. Her surname was registered as TREWERN not RICHARDS
Baptism - transcribed parish record
http://west-penwith.org.uk/paulbap5.htm1885 25 Nov Pollie Richards c/o Mary Annie TREWERNE [?] of Sheffield
"Polly Richards on the census records"
On the 1891 census she is Polly R TREWERN, 5 years granddaughter of Harry TREWERN.
1891 Census RG12/1856/118/21
Living at Sheffield Terrace, Sheffield, Penzance
TREWERN Harry Head Married 47 years General Labourer Born Cornwall Paul
TREWERN Mary Wife Married 45 years Born Cornwall Paul
TREWERN Mary H Dau Single 25 years Born Cornwall Paul
TREWERN Elizabeth M Dau Single 18 years Tailoress Born Cornwall Paul
TREWERN Polly R Grand daughter 5 years Scholar Born Cornwall Paul
1901 she is Polly RICHARDS living with grandparents.
http://www.freebmd.org.uk/cgi/search.plMarriages Jun 1906
JEFFERY Richard Penzance 5c/392
RICHARDS Pollie Penzance 5c/392
No father named on the parish record - NB link may not function in the future when database is updated.
http://www.cornwall-opc-database.org/search-database/more-in...Family stories are so hard to prove and so often events were covered up to meet the social niceties of the day.
The name Richard RICHARDS is common in the Australian indexes and even if you purchased the death certificates of the above men, only issue of their marriages would be listed on their death certificates.
Good luck with your search.