Use free/reduced eligibility from the most recent year that individual student data was collected.
This means you will use Data from the 2013-14 fiscal year as you implement CEP for the 2014-15 school year.
Further guidance is forthcoming on how this will be collected and determined in future years.
Online Resource
DA 12-1196 USAC Letter (PDF) - The purpose of this letter is to provide the USAC with guidance on the impact of the USDA's NSLP reimbursement mechanism, known as Community Eligibility Option (CEO) on the E-rate Program.