Many of the Cuban masters who defined 1997's Buena Vista Social Club are gone now. That fact makes these archival finds precious; the music makes them irresistible. Some are outtakes from the original sessions, like Omara Portuondo's lancing read of "Lágrimas Negras." Others emerged from the solo projects that followed, like "Pedacito de Papel," a guitar ballad cut with folk hero Eliades Ochoa. With Cuba finally opening up, here's hoping the heirs to this tradition can carry it forward.