In this episode, which aired in February 1991, the Huxtables are celebrating their 27th anniversary. This means that they were married in 1964. In the episode, It Comes and Goes, Clair refers to a Memorial Day weekend in 1967 when Sondra was three years old. This means that Sondra was born before May of 1964. If Cliff and Clair were married in February, 1964, then that means that either Sondra was born before they were married or Clair was pregnant with her when they got married!!!!