Before you can begin loading user account information into Identity Manager, you determine which know the following questions applies to your environment:
Is there an authoritative resource for all user IDs?
If yes, then loading user accounts into Identity Manager should be straightforward. Use that resource as your first resource, then load accounts from other resources, using correlation rules to link the accounts together.
Can a complete list of users be obtained from resources that overlap, but for which there is a correlation key?
If yes, then the process of loading user accounts will be similar. Be sure that the user accounts are loaded from the overlapping resources into Identity Manager before loading accounts from other resources.
Can a list of users be obtained from overlapping resources that do not have a correlation key?
If yes, then determine how a unique set of users can be discovered from those resources most easily. You will probably need to manually correlate and delete users for each resource.
If the answer is no to all these questions, then the process of loading accounts is problematic. Load user accounts as best you can, and plan to delegate creation of other Identity Manager users to departmental administrators or end-users.