Successive Timelines

When Time Patrol agents rectify a temporal alteration, they restore their preferred timeline in every way that matters although it is neither necessary nor possible for them to restore it in every detail. Thus:

in the original timeline, Lorenzo de Conti does not lead a flank attack at the Battle of Rignano;

in the alpha timeline, Lorenzo leads a flank attack, killing King Roger and his ablest son, thus changing the subsequent course of history;

in the beta timeline, Lorenzo leads the attack but is stunned by Everard although he does not fall from his horse and thus survives the battle which now has the same outcome as in the original timeline.

So far, so good, although Lorenzo, being a personal causal nexus, goes on to make another change, requiring a second Patrol intervention. Everard explains:

"'...by "randomness" I don't mean that things have taken this course without any cause. In human terms, people have done whatever they did for their own reasons. It just happens that what they did was different from what they did in our history. We've got to find that turning point - or fulcrum point - and see if we can't swing the lever back the way we want it to act.'" (The Shield Of Time, pp. 372-373)

But is there just one fulcrum point? I was taught that history comprised every individual exercising free will at every moment. If history is effectively rewound and played forward again, how can anyone guarantee that all those free choices will be as before? I thought this after reading "Delenda Est."

(Before the omnibus collection, "The Year Of The Ransom" would have been Vol III after "The Guardians of Time" and "Time Patrolman," as in the attached image.)