From all the evidence both here and on the older thread (much of it duplicated here) everything points to Sarah Helena Bougler being the daughter of William Boulger & Elizabeth Byrne born 1875 in Co, Kildare and registered as Sarah Jane. The fact that a baptism has not yet been found may be due to several factors (parents mixed marriage, other siblings had delayed baptisms & name changes, living in a different area (perhaps moved to Johnstown from Dublin not long before her birth)).
It looks as though Sarah is the Helena Sarah living in Londonderry City in 1901 as a lady’s nurse. Her sister Harriet was also a nurse (such a position would have needed little or no formal training). Her age isn’t too far out and the 2 Christian names she later used in America are here.
It may be that the family only stayed in Johnstown a few years before moving to Dublin which would explain confusion with Sarah’s place of birth. She may have also adjusted her year of birth to appear younger both for employment reasons, immigration reasons & to her husband (was be perhaps born after 1875?). In any case, such a thing is not uncommon.
You will likely have a good paper trail from the time Sarah left Ireland (passenger lists, marriage certificate, census records, Social Security file (not just the extract online), death certificate. Not sure how consistent age is in later records but it certainly varies from birth certificate to 1901 census. The one unfortunate thing is the day & month of birth on birth certificate quite different from S.S. recorded birthdate.
One possible reason might be that the date of birth on birth certificate is incorrect. It records birth as 9 Sept.1875 and registration as 22 Dec.1875. You now have 3 months to file a birth registration (can’t remember what it would have been in 1800s but think registering an early August birth at the end of December would have incurred a fine).
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1875/03081/2129791.pdfThe online R.C. parish register for Kill stops at 1880 for baptisms- I looked page by page 1875-1880 but couldn’t see one for Sarah but perhaps it was also a late baptism.
https://registers.nli.ie/parishes/0710The fact that the name, birthplace & birthdate fr Sarah in the S.S. record matches what you have noted as a baptismal record from a now forgotten source makes me wonder if you found that transcribed somewhere else (perhaps an online tree) and took it to be a baptism record.
