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Listen carefully to the Mutant Cleaver when he attack and you may notice him shouting "Hey You Guys!" This is likely a reference to Sloth from The Goonies, who bears a resemblance to the Cleaver.
1 of the loading screens mentions the date "April 2031". If you take April and switch 2031 to 0213, you get the release date for the game, April 2nd 2013.