I’ll stick with the theory that first off they used high sulphur steel plates, too brittle in the cold, and that they switch builders plates with the Olympic.
One of the first things they did after bringing up some salvaged plates was to run tests on them and it was found that the samples showed average toughness of 55 MPa-m**0.5 at 0°C....that was actually a very acceptable value for this application. It was the rivets.....