Outlook 2000 Calendar not showing all events

We use a number of shared calendars for managing conference rooms,
vacations, install schedules, and such.
Lately with a lot of people using up their vacation time, the vacation
calendar has become very busy. It has been brought to my attention that not
all events are visible when focused on a particular day / date. i.e. I had
a manager enter a vacation day for an employee, but it never appeared on the
day / date for him, but if I do an advanced search for that employee I can
see that the manager actually entered the vacation day 4 times. Any ideas.
I have verified that there is no filtering turned on. Is there a known
limit to the number of calendar events for one day? I can only see 16
events, even though I know there are more.

Exchange Server 5.5-SP4
Outlook 2000 and Outlook 2003 exhibits the same behavior.