Complex sentence: Tom and Helen married in 1951 but it is confirmed in the later seasons that Tom and Helen was married around 1954, but on the episode, "The Other Woman" (aired in 1979) it was originally confirmed they were married around 1951.
Split into simpler sentences: Tom and Helen marry in 1951, but it is confirmed in the later seasons that Tom and Helen are married around 1954. However, on the episode "The Other Woman" (aired in 1979) it was originally confirmed they were married around 1951.