From the Notes client, users have provided permission for their colleagues to read their calendars. (On the Mac Notes Client: Preferences/Calendar & To Do/Access & Delegation)
As Administrator of the SmartCloud account, I have enabled calendar detail collection (Admin/Manage Organization/IBM Smartcloud Notes/Account settings//Email and calendar options)
Users still cannot see any details of others' calendar.
(This is a cloud-only environment, not hybrid.)
Is there something else to be done?
RESOLVED: Turns out enabling calendar detail collection only affects new calendar events going forward, not existing ones.