Problem: You have events on your calendar older than a specific amount of time, usually one year, sometimes as short as two weeks, which are not shown.
All events that are synchronized to your device are visible in DigiCal. However, the synchronization itself is performed by other apps, usually system apps that came preinstalled. These sync "providers" may impose certain limits on the age of your events in order to avoid having to synchronize a potentially very large number of events.
Unfortunately, DigiCal cannot change the behavior of these sync providers. We do not have any influence on the limits they impose.
The most common sync provider for Google Calendar only synchronizes your calendar one year into the past. As such, any events on your calendars that are older than one year may not be synchronized to your device.
Exchange & Outlook.com
Many sync providers for Microsoft Exchange or Outlook.com accounts also impose limits on the age of your events. Often, this limit will be set to two weeks by default. In this case, any events older than two weeks at the moment you add your account may not be synchronized. This limit is sometimes configurable, in which case you can change it when you initially add the account by clicking "Advanced settings", "Manual setup", or a similar option.