I'm a new player, and my understanding of how this game handles the random ancillaries and events is that they're supposed to be based on a continuous seed that's saved in your save game file so that you can't just savescum your way to desirable results. However, my experimentation has shown that this currently isn't the case.
I can demonstrate this in my current Cao Cao campaign by watching a battle between the A.I. Yuan Shu and Lu Bu after I pass on turn 17.
1) Load in on turn 16.
2) Pass two turns to reach turn 18. I can see the outcome of the battle and also gained a Wooden Dog ancillary.
3) Loading the turn 17 autosave and passing to turn 18 leaves Yuan Shu with the exact same number of people left alive in his army as in step 2, only this time I don't get the Wooden Dog.
Reloading turn 16 again and passing always gets me the Wooden Dog on turn 18, but loading from turn 17 does not. I've also seen this with events, where passing two turns gets an event but loading the autosave from the turn before and passing gives a different event or no event at all.
I learned this is how things are working the hard way in my current campaign. After fighting a successful battle I ended my turn and got a cool ancillary and a general with fantastic traits spawned in my faction. However, I immediately misclicked with my army and sent them to the wrong spot, so I loaded up the autosave so I could do it right. This time though, instead of my previous ancillary and general I was presented with the common Eavesdropper, and I have no way to get back to my previously fantastic result.
Is this working as intended?