Just found this on the nestle-purina aeroplan pin entry site:
Please note that effective August 31, 2012, Purina® products will no longer feature PIN numbers to be eligible for Aeroplan Miles. All Purina PIN numbers must be entered online at nestle-aeroplan.ca prior to December 31, 2012 in order for the miles to be credited to the member’s Aeroplan Account

eek!