I found her!
Here in GenealogyBank’s Social Security Death Index (SSDI), I found the record for Marcia (Leavitt) Dyer.
She was born on 27 September 1880 and died on 15 May 1968.
But – Marcia Leavitt’s online family tree said she was born 31 March 1881. Why aren’t these records matching up with each other?
Were there two different Marcia Leavitts – born within months of each other? I needed to find out.
So I retraced the research others had done.
Look closely at her birth certificate. I think I’ve found the source of the confusion.
It doesn’t say that she was born on that date – it says her birth was “reported for year ending Mar. 31, 1881” – but no specific date was given. Some family historian had probably seen this record and entered that date on her family tree as her actual birth date.
Genealogy Tip: when you see dates on a family tree that don’t match what your own research has turned up, dig deeper, trying to find as many primary sources as you can, to solve the discrepancy.