Sivia (Sadie) Varbalow (Stillman) - Sadie Varbalow's birthdate

I'm not sure where to put this so I will post here. The 1900 US Census for the Varbalow family (household of Hyman Varbalow, 1207 Fifth Street, Philadelphia, PA, Enumeration District 44 Sheet 2 B) asks for month and year of birth. Sadie is recorded as age 39, born March, 1861. The informant is unknown. Sadie Varbalow's death certificate (I have attached a copy in medla) February 25, 1934, Atlantic County, New Jersey records her birthdate as December 15, 1857, age 76 years, 3 months, 10 days. The informant is her son Joseph Varbalow. Without access to a birth record for Sadie (and knowing that probably none exists) there is no way to know which is correct.