Anyway, here's my own version of a code breaking puzzle using event numbers...
https://barako-the-pirate.itch.io/code-breaker
As you can see, you don't need parallel events for this particular thing you wanna do. Everything is done through a common event and the boxes in which you input numbers in. Far, far less for you to maintain and create.
Hopefully it's useful to you. If not, it's certainly useful for me! Your game gave me great ideas for number inputting puzzles in my own games!