Complex sentence: Her countless intervals on board dated from 6th March to 10th May 1974, from 16th December 1975 to September 1976, a brief period of a month in March 1977, and finally from 21st September to 17th October 1978.
Split into simpler sentences: Her countless intervals on board dated from 6th March to 10th May 1974, from 16th December 1975 to September 1976. A brief period of a month in March 1977, and finally from 21st September to 17th October 1978.