For efficiency reasons an Acl may be loaded and
not contain
entries for every Sid in the system. If an Acl has been loaded
and does not represent every Sid, all methods of the Acl can only
be used within the limited scope of the Sid instances it actually
represents.
It is normal to load an Acl for only particular Sids if read-only
authorization decisions are being made. However, if user interface reporting or
modification of Acls are desired, an Acl should be loaded with
all Sids. This method denotes whether or not the specified Sids
have been loaded or not.