You create a planning meeting for four people. Later, a fifth name appears. Before blaming a calendar error, check whether the invitation allowed guests to bring in other participants.
For an event you can edit in Google Calendar on a computer, inspect the guest permissions. Google documents an “invite others” checkbox under “Guests can”. Clear it if you want additions to go through you, then save the event. Available controls depend on your role and the event type.
Set a clear rule for additions
For a small planning session, a useful description might be: “If someone else should attend, ask the organiser to add them.” This tells guests what to do without giving them control over the whole event. It is an example of wording, not a confidentiality guarantee.
Keep invitations out of public channels. A permission setting is not a barrier to someone copying the time, description or meeting link. Do not place unnecessary private details in the invitation simply because the guest list is short.
Check the list and the linked files
After changing the setting, reopen the event and inspect the saved choice and current names. Preventing new invitations does not establish that every person already listed should remain. Review unfamiliar names before removing anyone, especially on a shared work calendar.
Check linked documents separately using their own sharing controls. The guest list is not an inventory of every route to those files. If learning the controls, use a clearly labelled test event with a willing participant and no private attachments. Delete the test afterwards so it is not mistaken for a real meeting.