If your Google Calendar sync is not syncing all of the data on your calendars the following suggestion was sent in by a user and it corrected this issue.

Go into Google calendar on your computer's web browser
and do an export of all calendar data and then, do an import using the
file that you created in the export,

it resets something in the Google calendar. 

Then, when you do a sync it will pick up all data in the Google calendar as far back as you have data.

Another option is to go into the Informant settings, sync accounts, Google Calendar, sync options, and set the range of data that you wish to sync.  Shorter ranges of data will sync faster, while larger ranges of data will take longer to sync but provide more data.