There more info here: http://www.keacher.com/1060/how-i-got-to-my-first-sale/

The first result for "blurity serial number" points to https://www.trademarkia.com/blurity-77870929.html

Edit: Entering the serial number does indeed produce the easter egg dialog, with a coupon code that still works. BTW, there is a typo on the buy page 'regsitration'.