If this is happening, then you may notice missing, non-existent and/or incorrect entries.
In order for some GAL entries to show up properly you may need to turn off Cached Exchange Mode.
Please visit the document on How to turn on or off Cached Exchange Mode for (Outlook 2010, and Outlook 20).
Outlook 2011 does not use Exchange Cached mode and directly connects to the Global Address Book (GAL) via LDAP connection.
In this case your global address book will update each time Send/Receive is pressed.
This next post is going to talk in detail about GAL segmentation setup in Office 365.