According to House Steiner (The Lyran Commonwealth) and Tactics of Duty, the Fourth Royal Guards were destroyed on Caledonia after fighting the Dracs for 7 years.
According to p. 41 of the Handbook: House Steiner and Second Succession War, they were destroyed on New Caledonia after fighting for 7 years.
Both planets appear to exist in very different parts of the Lyran Commonwealth.
Which one is the site of the death of the Fourth?