What does the phrase "method of verification" mean?

It refers to the method, mechanism, or essence of the verification process... The meaning is the same.

So, I'm not claiming that morale drops should be verified in any specific way – yes, the question is about verifying the save file, but if the save file includes morale drops, what do you suggest?

It's difficult to verify morale drops. That is, if the verifier gets the same result, that's great. If not, it doesn't mean that it couldn't have happened.

Of course, there are obvious points to pay attention to: the morale level of the troops (if it's neutral or negative, then there's no point in continuing the discussion), the presence of artifacts that increase/decrease morale, the use of spells (if mana is available), etc. This is complex, but theoretically verifiable.

However, when we have positive morale, the question of the drop is reduced to probability theory. For example, we have a long battle – the number of rounds is statistically significant. Then, we can assess whether the probability of the drop corresponds to what the theory says.

If it does, the issue can be closed in favor of the player because it is impossible to verify the drop/non-drop of morale in a specific round of the battle. If it doesn't correspond (significantly exceeds), then we need to think... But this is a very rare case, so it is not advisable to solve this problem at the moment.