From May 22, 1948 to October 13, 1958, multiple charts were published, which explains the overlap in the dates of the charts. The 1942 "Harlem Hit Parade" chart, based on juke box plays, became the "Race Records Juke Box" chart in 1945, and the "Race Record Best Sellers" chart, based on sales, began in parallel in 1948. They were renamed as R&B charts in 1949. A third, "Jockeys" chart, based on radio airplay, was introduced in 1955, and a unified chart was only introduced in 1958. Because of the existence of multiple charts, some dates had more than one number-one song during the week.
From November 30, 1963 to January 23, 1965 there was no Billboard R&B singles chart. Some publications have used Cashbox magazine's stats in their place. No specific reason has ever been given as to why Billboard ceased releasing R&B charts, but the prevailing wisdom is that the chart methodology used was being questioned, since more and more white acts were reaching number-one on the R&B chart. According to researcher Joel Whitburn, "there was so much crossover of titles between the R&B and pop singles (Hot 100) charts that Billboard considered the charts to be too similar. This does not mean that R&B artists stopped turning out hits. After all, it was during this 14-month period that Motown established itself as an R&B institution."