This is not a bug but a limitation of the sync adapter.

If you use Google Calendar, old events (older than 12 months) are usually only available online in a web browser.

To get older events to sync to Android follow these steps (and repeat every 12 months):

  1. Go to Google Calendar with a desktop/PC web browser
  2. export your calendars 
  3. re-import the calendars

Unfortunately, we are not aware of such a solution for future events.