A published timetable added as a Calendar subscription remains controlled by its provider. If an event looks wrong, changing your own calendar settings cannot rewrite the provider’s event. First determine whether the problem is stale information, the wrong feed or an expectation of editing access.

In Calendar on Mac, select the subscription in the calendar list and open Get Info. Check its name and web address against the trusted source that supplied it. Avoid adding a second copy while the original subscription’s identity is still uncertain.

Check location and refresh behaviour

Apple’s subscription setup offers a location choice. An iCloud subscription can be available on devices configured for that iCloud account, while On My Mac stores the subscription on that computer. Check this if the timetable appears on one device but not another.

Review Auto-refresh in the subscription’s information. Choose an interval suitable for the schedule, and use View, Refresh Calendars for a manual check. Record the time of the test so you can distinguish a recent refresh attempt from an old screenshot.

If Calendar shows a warning symbol, Apple advises checking connectivity and whether the calendar was deleted or moved. Compare the subscription address with the provider’s current published address before replacing anything.

Verify the event with its owner

Compare one specific event with the provider’s published information. Use its date, title and start time, not merely the appearance of the month view. If the provider’s own feed still contains the old details, repeatedly refreshing your Mac will not create a correction.

Subscriptions are not editable shared calendars. If the work requires several people to maintain events, arrange the appropriate shared-calendar workflow with the owner rather than trying to edit the subscribed copy.

Check alert settings separately from freshness. Receiving no reminder does not prove the calendar failed to update, because a subscription can be configured to ignore alerts.

Once the correct feed and behaviour are established, keep one recognisable subscription and note its source. Remove an obsolete subscription only after confirming which copy contains the schedule you intend to follow.

References: Apple: subscribed calendars, Apple: refreshing calendars.