I'm working the Patuca and some time back I definitely noticed the change described in these posts. Suddenly they were Armed Guards and not Prize Crews anymore.
I had always enjoyed reading the latter term, as it reminded me of the adventures of Patrick O'Brian's Captain Jack Aubrey and Doctor Stephen Maturin, aboard various Royal Navy vessels at the time of the Napoleonic wars. Whenever an enemy ship was captured a prize crew was set aboard to steer her to the nearest allied port. Each man on the capturing ship received a fixed fraction of the value of the prize ship, including head money for prisoners, and O'Brian loved to show each man totting up his share to the last fraction of a shilling.
Now, I don't suppose that kind of thing went on in the early 20th century ~ I guess the term was a vestige of former naval custom which the Admiralty finally decided to officially change.