You can import the events of one calendar into your All-in-One Event Calendar as long as you can get the calendar's .ics feed URL. This tutorial will explain how to get the .ics feed URL from one All-in-One Event Calendar and add it to another All-in-One Event Calendar.
To get the calendar feed from calendar.gsu.edu, follow the directions in the article Get the calendar feed from calendar.gsu.edu
Get the .ics feed
When viewing a Calendar you wish to export:
Right-Click Subscribe at the bottom of the Calendar or widget, then click Copy Link Location.
Add the feed to your calendar
Open the settings of the destination Calendar and go to the “Calendar Feed” page.
Paste the link you copied into the “Feed URL” field. Choose the Category in which to import your event. If you need a new category, create it first using “Event Categories”. Add any desired Tags. Click Add Subscription to add the feed to your Calendar.
Click Refresh on the feed to complete the import.
A message will appear showing how many events have been imported. Click 'Update Settings' and your new feed will be saved.