Ay 2015-2016 return filed on 15/11/2017 how it is possible??

Today I have come across a ITR Ack. for AY 2015-2016 which was filed earlier but the most surprising thing is that when the last most date after which that ITR can not be e-filed was 31st March 2017 , then how it is possible that it is filed on 15/11/2017 with original acknowledgement no -305274200151117 and PAN no- BLHPJ2036C Which I already checked with income tax website and it and this ack. no matched with this PAN no. so anybody please clarify that how this is possible to e file this return.