My impression was that ASCAP was the older association, and started with the New York Tin Pan Alley trade of mostly standards, and BMI was the newer of the 2, and started out grabbing a lot of the WWII and post WWII trade from the glut of new independent record labels signing new singing artists, which included "Race Music, C&W music, Gospel, and other genre niches. That included R&B. Of my 40,000 singles and couple thousand LPs, the great bulk of my r&B group and single artist songs that were written by the newer, non mainstream, non major label, songs that were NOT old standards were registered with BMI, rather than ASCAP. Probably 95% of my R&B and ;60s Soul songs were BMI. It was only when groups and single artists sang remakes of old standards, that the songs were registered by ASCAP.