This is telescoping.
If you are ever perusing the LCBO shelves and see someone performing this ritual, you are in the presence of a veteran beer purchaser.
Simply put, those date codes on the bottom of each can are important—beer is meant to be consumed fresh, and the longer it sits the further it gets from its intended taste.
This is especially true for IPA's. Hops degrade over time, creating unwanted malty/caramel flavours that dominate the beer. We brew mostly IPA's and have become obsessed with making sure the freshest, best version makes it into your hands.