How can group membership change over time?¶

Members can join, leave, be removed, return or change accounts, so the current participant list is not a reliable history of who could access a particular message.

Membership is a timeline¶

Invitation links and administrator actions can add users. Account identifiers, telephone numbers and display names may change. A restored account or reused number can complicate continuity, while platform rules determine whether new members see earlier content.

Preserve system join, leave and removal messages, invitation and administrator events, stable account and group IDs, roles and timestamps. Provider or organisational logs may retain history no longer visible in the chat.

Test access at the message time¶

Compare each membership interval with the relevant communication. A current member may not have seen earlier history; a former member may retain messages received before leaving.

Report present membership and historical access separately. Avoid saying all current members received an old message unless the service behaviour and individual membership dates support that conclusion.