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):
- Go to Google Calendar with a desktop/PC web browser
- export your calendars
- re-import the calendars
Unfortunately, we are not aware of such a solution for future events.