CALIFORNIA EVIDENCE: CIVIL AND CRIMINAL
...Privileges
......Waiver of Privilege
.........Waiver of Jointly Held Privilege
3 Cards On This Topic:

Waiver by one possessor of jointly held privilege does not waive for all.

For jointly held privilege, waiver by one privilege holder does not prevent other holders from claiming privilege.

D's waiver of attorney-client privilege not binding on joint holder of privilege.