Certainly.

For years I maintained a ragged spiral notebook of video game info which contained among other things some extensive, entirely handwritten reverse engineering of the password systems for MegaMan 2 and Metal Gear.

http://www.mmhp.net/Passwords/MM2/

Check boxes and see how the pattern changes, which is like how we wrote down the codes when we were kids after we beat a boss. It's easy to see that generally only the position of one red dot changes after each level. So it makes it very easy to brute force more options.

Not hacking the system properly, but enough so that you could get past levels you were stuck on.

When Mega Man 3 came out, I decided I was going to the "the first" to figure out how its password system worked. But it was incredibly easy. It was already published in the magazine before I could write my letter.