Complex sentence: The most notable of these instances occurred immediately following Lennon's death on 8 December 1980: the song entered at the No.2 spot--falling just short of becoming a "Christmas number one"--and remained on the chart for nine weeks.
Split into simpler sentences: The most notable of these instances occurred immediately following Lennon's death on 8 December 1980. The song entered at number 2, falling just short of becoming a "Christmas number one", and remained on the chart for nine weeks.