I don't know if this might be of significance, but in 1861, there is a Catherine Pugh in Dolgelley, born 1831, who has three children: Sarah and Ann, both born in London, and Evan in Dolgelley.
FindMyPast has her as a widow, although it looks like married changed to unmarried.
In 1871, she is Sarah Jane Pugh, born Middlesex in 1855.
There was a Sarah Jane Williams Pugh born in Lambeth (although Surrey) in 1855 with no mother's maiden name, and an Evan was born in Dolgelley in 1859, also with no mmn.
I was wondering if this might have caused the confusion about the birth place and the name of the father etc.
David