It's based on the save system. The idea is to use save A (before Nameless event just to be safe) to create B, load B, do your decision and create C based on A to repeat.
Also on regards to the new event: This trick won't work after the first event. I got Nameless saying that I'm repeating the second event even though I was using different safefiles based on B.
So yeah keep save A like a treasure if you really want all the Nameless content. Just be warned, I didn't used a C based safefile to access the second event yet, but it should do the trick.