Apple 1-year warranty without receipt
I'm thinking about purchasing a used iPad and most sellers don't have the receipt but I checked on the support coverage page (https://selfsolve.apple.com/agreementWarrantyDynamic.do) and the serial number says there's still a couple months warranty remaining.
My question is, if I buy a used device without receipt, will I be eligible for the remaining months of warranty or do I need to have the receipt?
Thanks!