Orange Juice did not even exist in the United States until after World War Two, and before the War, oranges were only found in California and Florida.
The sous chef asks Alfred and the other students the name of the soup that was previously leek and potato soup. After one them correctly answers the questions he asks if they have the instructions in front of them. However, the name, "vichyssoise" and the recipe are clearly written on the blackboard in the front of the room.
Mrs Patmore has a rip in her apron on the bottom, in the middle, straight up, 6" long. When she's shown the repair by the seamstress, it's the seam on the corner she's shown, not the center where we originally saw the ripped cloth. Also, the servants are amazed and in awe of the electric sewing machine. This was 1922, electric machines had been around since 1890, hardly something none of them would have never seen before.