Can anyone help me figure something out.

Hey guys I know it's been a long time but, I'm confused. I tried to Jumpstart my love with the fandom again, and was loving it until I reached a certain episode. The episode's name is twilight's kingdom. It makes celestia a liar. She states that starswirl didn't understand friendship. Yet how do you befriend someone if you don't understand friendshipship.
There is also the part where they give up their powers
That they state about tirek not knowing their being a new princess in the last thousand years. Why do they not get rid of everything showcasing twilight as a princess. They had an entire day to do it yet it's still there.
Also why does it show cadence as a teen when twilight was a filly, because as I had just pointed out using cannonverse that she is really old. If anyone can provide answers it would be greatly appreciated. Please only use logical reasoning and examples from the show in your explanation.