Siemens SK65 Software User's Manual page 60

Appointments in your phone calendar that are
older than the number of days that you specify in
the Keep Appointments field are removed from
your phone. The appointments can be restored,
however, if you set the Keep Appointments field
to a longer period of time. When you increase the
amount of time in this field, any appointments in
your calendar during that period of time appear in
your phone calendar.
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