There must be something we don’t know about the way these gospel groups count their members.
The term Gospel quartet refers to several different traditions of harmony singing. Its origins are varied, including 4-part hymn singing, shape note singing, barbershop quartets, jubilee songs, spirituals, and other Gospel songs.
Gospel quartets sing in four-part harmony, with parts given to a tenor, or highest part; lead, which usually takes the melody; baritone, which blends the sounds and adds richness; and the bass, or lowest part. It is not uncommon for some quartets to switch parts between members for given songs.