The truth is when we are maturing and changing, we know that we are changing, because we can notice how we now overlook the same things that used to get us worked up before. Just like you said, what would have gotten you angry and made you reply actually didn't get you angry this time around.

Even though we can't all see ourselves through our eyes alone, we have other people who can be our eyes, but the caveat is that we can't depend on everyone because some people are not honest. So what I do is I have few friends in my corner who when they tell me I have changed for good or bad I believe them because I know these people genuinely love me and are really looking out for me.