Examples include: inability of USCIS to verify I-94 issuance in connection with a benefit such as the issuance of an Employment Authorization Document (EAD) for someone who entered in April; inability to view a record of admission.
CBP Response: The automated I-94 process was not initiated until May 2013. The alien discussed in the above question was admitted last April and should have been issued a paper Form I-94. If this alien was not issued a paper Form I-94 through an oversight or error on the part of the government, she/he should go to the nearest Deferred Inspections Office.
source: CBP/AILA Southern California Chapter Liaison Meeting September 24, 2013