You are quite correct. NY records are very incomplete. However, here's what I have. It's based on the original work of Walter Smith [author of The Sterry Family of America] and Carolyn Magruder, who along with her sister Anne Sterry Henges, worked with Walter for many years. I have a lot of additional information on Silas Sterry's presumed father, William Sterry. Easier to email me direct on firstname.lastname@example.org
Silas C Sterry is the probable son of William Sterry [1794-aft 1852] and Eleanor.
No birth record has been located for Silas and his birth and parent information relies on census information. The census record [except for the 1850 which is assumed to be an error] states he was born in New York abt 1821. There are only three Sterry families living in New York in the 1830 census and only one with a male child of about 9 years: that of William Sterry at Kortright, Delaware. It is very probable therefore that Silas is William's son. In the 1830 census Silas had a younger sister aged under 5 years. Later census and vital records indicate this is almost certainly Delia.
Further information on the marriage of Silas and Marion [researched at NY State Archives, Albany by Carolyn Magruder]:
Delaware County Marriages, compiled by Minnie Cowan, Vol 2
1849 Oct 22 at the Head of Delaware by Rev. W.A. Curtis
Silas C Sterry of Stamford and Mariah J. Underwood
Delaware County Church Records, Worden
At the house of Mr J.R. Baldwin, Stamford, Silas C. Sterry and Miss Marion J. Underwood, late of Canaan, Connecticut. Present were Mrs Underwood, the mother, Mrs J.R. Baldwin, the sister, and J.R. Baldwin, brother-in-law of the bride.