Billboard R&B Number-One Songs, 1970 to 1989 Quiz

Every song to finish a year at number one on Billboard's R&B/hip-hop year-end chart between 1970 to 1989: 20 years, one per year, taken from the same published table as the complete run. This is the era cut, for when the full set from 1946 is more than you want in one sitting. Name each from its year, pick the year's real number one from a group of genuine chart-toppers, match each song to the artist credited with it, sort a selection into the order they led, or tap the era's number ones out of a grid seeded with real number ones of the same chart from other eras. Parsed verbatim from the published year-end table; no answer is named here.