As a genealogist I'm not above looking gift horses in the mouth. There are two critical diarists in New Hampshire whose entries have helped me. Joseph Tate was the schoolmaster of Somersworth, N.H. and kept a diary with all Somersworth families information from 1740 to 1778. The original is at the NEHGS Library in Boston and was reprinted in the New England Historical Genealogical Register in volumes 73 and 74. One entry reads " Mr. Jno. Cromwel of Dover Dy'd on Saturday, May ye 11th 1776 & Lydia his wife dy'd on Monday May 13, 1776. Both Buried in One Grave." That's the only source for their deaths. However, couldn't Master Tate note Lydia's maiden name? Just one more line "she was the daughter of X."