Complex sentence: From late 2002 onwards, these sales began to significantly decline: by the start of 2004, they had dropped to their lowest level in 35 years, with singles needing to sell only 35,000 copies to reach number one.
Split into simpler sentences: From late 2002 onwards, these sales began to significantly decline. By the start of 2004, they had dropped to their lowest level in 35 years, with singles needing to sell only 35,000 copies to reach number one.