It was reasonably common in the floppy disk era. Some games allowed you to play for a set amount of time, after which it asked you for something external to the game itself. Some examples I remember:
- Dune 2 asked for some units stats that could be found in the games manual
- Day of the Tentacle needed you to complete a battery blueprint sketch in game. The missing info could be found in the manual
- Monkey Island 2 asked for a voodoo recipe. To find the correct measurements, you had to spin two overlaid sheets to align something, which revealed a value.
All of the above could of course be copied and/or guessed, but it did at least introduce some bar of entry.


