Hi. 1. There's no room for commas between the Subject (--Nothing you could have done ...) and the Verb (+ would have changed...) as well as between the Verb and the Object (+ the events). 2. ---Nothing would have changed the events ---Nothing (...) would have changed the events ---Nothing (---that you could have done---) would have changed the events We could transform it as ---"Even if you had done anything (that) you could (do/ have done), this would have not changed the course of events (anyway)". I just hope you understand your issue.

Perhaps you're more knowledgeable than I regarding this, but in the example you give here, "we had booked our flight earlier" is a single condition. In the question you ask, "Nothing you could have done" specifies ALL POSSIBLE CONDITIONS. Again, this doesn't seem to fit into the definition of a conditional, as I understand it, but grammar is not my strong point. Is "You couldn't have done anything to change the course of events." a conditional? Because, to me, it means exactly the same thing as your original statement.

it emphasizes that something will happen, would happen or would have happened whatever the condition. For examples: Even if we had booked our flight earlier, it wouldn't have been cheaper.

I'm not a grammarian, but I don't see how this can be a conditional. A conditional requires a specific condition in order to have a particular outcome. In this statement, ANY condition (anything that the person might have done) would lead to the SAME outcome (no possible change in the course of events). An equivalent statement to this could be: "You couldn't have done anything to change the course of events."