This is a new installation that switched from Lotus Notes two weeks ago
This makes it even more likely that the mailboxes are broken. This is not to besmirch the folks that did the migration. This particular problem is quite common with migrated data.
Outlook has no problems showing these other users' calendars. (I can send you a screen shot...)
A thought - are you sure Outlook is actually showing you the details from these other user's calendars? Outlook has a fallback mechanism for when it can't get the Calendar folder. It takes the information published in the user's Free/Busy and "fakes" a calendar, which for many purposes is good enough. You can tell when you're getting this fake calendar because you can't get any details, like subject, locations, or meeting notes.