As another example, in January 2013, I discovered a cheat code in the SNES RPG Breath of Fire 1 that allows you to create a save file at a few key locations in the story. This cheat code sat hidden for about 20 years, and it wasn't until I came along and reverse engineered the game that it showed up.
Link to it: click me. Sorry for the quality; it is a really difficult thing to record when your only recording device is an iPad and there was nobody home at the time. Not to mention how hard it is to do that controller sequence and record with only two hands.