I don’t know any airline that will board passengers after the flight is closed. There is a very good reason for this, it’s called OTP and the knock on effect it has down the network. If you are late, and I couldn’t give a rats a**e what the reason is, you don’t get on. For self-loading freight to compare denied boarding because “they” were late with an airlines OTP may seem fare to them but frankly is irrelevant unless the circumstances are known for the late departure or arrival. Who knows it could have been caused by a late passenger a couple of sectors ago.