I have just spent a day in Krigsarkivet, in preparation for my May talk about some overlooked sources concerning Armfeldt's campaign in 1718. One of the volumes I looked at contains incoming letters to Lt. General de la Barre. According to Svante Hedin's bibliography Armfeldts fälttåg mot Trondheim 1718-1719 (1986) it should contain no less than ten letters from Charles XII, dated 1 October 1717 to 19 May 1718.
This sounded rather curiuos to me and turned out to be incorrect. The letters were not signed Carolus but rather C. Feif...
Despite the fact that the field archive of Armfeldt's army appears to have been lost the records from the campaign are very extensive. The documents concerning supply matters are very informative and detailed to the last penny.