This seems like as good an idea as any. There is a Thomas Kissick in Boston at the same time as my William, which I initially took to be his father. This Thomas married Sarah Sanders, from another prominent Boston family, in 1728. They had a son by the name of John born in 1730, but I have been unable to find out anything else about this family. I had thought it strange that they would have had children so far apart in age, with no others recorded. I have found no other records of this Thomas or of John that I can definitively connect with them.
Finding the British Admiralty records seems to refute the connection to Thomas, if the Williams that I am speaking of are all one and the same. I know that William who married Elizabeth Whitman died before 1798, as she conveys a parcel of land to her brother and is shown to be a widow at the time. There does not seem to be any mention of William after the Revolutionary War, hence my suggestion that he went back to his birth home after the Admiralty trial.
William and Elizabeth have children in 1769, 1771, 1773, 1774, 1776 and their last child's birth year is unknown. This information would seem to correspond to the wartime service commencing. The Kissick women seemed to marry later than was common and this last daughter married in Boston in 1805. That allows me to estimate her age based on her sisters ages at their marriages at somewhere in her mid-20s. So that puts her probable birth year at about 1780 or therabouts. Which might make sense in light of the war.