A rule of multiples

Anyone who has heard any of these live at least once will have heard them live several times: Peter, Paul and Mary; Pete Seeger; Conway Twitty; Loretta Lynn; the Statler Brothers; Marcia Ball; Van Morrison; Junior Brown; Don Walser; the Cornell Hurd Band; Alvin Crow; the Geezinslaws; Bob Dylan; Thelonious Monk; the Supremes (Motown sent them everywhere, with a huge investment in evening gowns and gloves); Sly and the Family Stone; Johnny Degollado; Ruben Ramos and his band; Joe Ely; Dave Van Ronk; the Ike and Tina Turner Review; Ponty Bone; Toni Price; the Isley Brothers; and many more. These are just the ones that leap to mind because I've heard them multiple multiple times, not just "more than once."