In a newspaper article, I found the info that Lillian Hayman was coming back to the show after a 2 year absence. I found another article from May 1971 which mentionned that Lillian Hayman played the role of Sadie until recently. She had apparently already left briefly as in September 1970 she is mentionned as being back. Esther Rolle played the role briefly at some time. It's not very clear.
During the same month, last original cast member Doris Belack left and Anna was recast with Kathleen Maguire.