How do I retain calendar appointments in months already past?

It appears that months after an appointment is listed on my Outlook calendar,
the calendar is cleared. I'm not sure how much lag time, but I know I have
sometimes gone back say 6 months to reconstruct the dates of a meeting and
there are no appointments listed (except for reoccurring appointments, for
some reason?). Apparently, it clears appointments at some point when they are
6 months old or so? Is there a way to turn the clearing function off, or
maybe extend the clear date to 12 or 15 months? I can't seem to find anything
about this on MS Help. Thank you.