William Chew's traditional death date of 28 Feb 1709 appears to be based on the last public record that mentions him--the will of Thomas Smooth. I don't have a reference to this will, but here is what the the Smoot Family Web Site says about Thomas Smooth's estate:
"25 Apr 1709 Maryland Probate Records. 29.225 Charles County. #56130. Accounting of estate of Thomas SMOOTH, decd. A second inventory #7899. Total equivalent to #51865. Payments to: [partial extraction]. John ROGERS, William MUSGROVE, Ralph SHAW, Elizabeth HAWKINS, Charles MUSGROVE, Claborn LOMAX, Mr. GRESHAM, Saml. HANSON, Mr. Edmund HOWARD, Mr. William CHEW, John STANBURY, Charles JONES, John BRADSHAW, Mrs. Elizabeth BONNER per Rev. Jonathan WHITE, Capt. Thomas DENT executor of William DENT, Vestry of Port Tobacco. Administrator: Barton SMOOTH."