Distribution Groups

Hi

I created a new distribution group (Exchange 2010) 2 days ago and populated it with the relevant staff members.  However, the GAL is picking up the new group, but not all of the staff members are there!  Any ideas why this might be happening and how I can get it sorted out?

For info, our AD is running on Server 2003, soon to be upgraded to 2012.

Regards

Gary