Report for historical assignments and table UNSAccountInUNSGroup

The standard report VI_Person_Overview_With_History show amongst other things historical assignments of UNSAccounts ang UNSGroups, with name of UNSGroup and assigned from and assigned until time, using CreationTime and DeletionTime. I would also like to add info about what user assigned the UNSGroups. I thought CreationUser would solve this, but when using that column it only says user SA, even when the UNSGroup is assigned manually to a user account in the Manager. Is there a way to get info about what user actually added the role to a user account?