While Dean is telling Sam he has to stay and survive, the bag with the goofer dust in it changes positions on the floor.
If Kevin is in Missouri (as suggested by the registration on the ship & the radio voice), there is no possibility for him to wake up to full daylight at 5 AM in January, as is shown in the opening scene. Sunrise would be around 7.30 AM in mid-January, making full daylight impossible until at least half an hour to an hour later.
If the Men of Letters bunker was closed from 1958 until reopened by Sam and Dean in 2013, there would be no way for there to be memory foam mattresses since it wasn't developed until the 70s by NASA, and the first memory foam mattress being on the market in 1991.