Do you know what Cunard’s intention was?
No of course I don't.
As a polo shirt is a collared shirt ( in my humble opinion) that is what I will sometimes wear until Cunard tell me otherwise.
I will make my own interpretation of the dress code. As should other people and not bow down to the dress code police.
I intend to go on my cruise and fully enjoy myself. I will adhere to the correct dress codes on the correct nights.