In Eirik Hornborg's biography Karolinen Armfelt och kampen om Finland under det stora nordiska kriget (1953) the author admits that he does not know what Armfeldt did in the months preceding his appointment as Aide-de-camp to Major General Cronhjort in December 1700. Hornborg, who used Cronhjort's letters to Charles XII, seems to have overlooked Governor Vellingk's letters to the King. On 10 December 1700 the Governor wrote to Charles about Captain Carl Gustaf Armfeldt, who Vellingk "last summer" had awarded the lease of the estate Gatchina because he was an able man, who had endured a lot of hardship in order to make himself suitable for Royal service. Unfortunately the previous leaseholder Albrecht Düring made difficulties. Vellingk pointed out that Düring's father had never served the Crown and Düring himself had left Ingria as soon as war broke out, while Armfeldt could personally describe to the King not only his 10 campaigns during the last "War of Brabant" but also how he since the Great Northern War broke out had taken part in real actions and had risked his life without receiving any payment. Surely the King would rather grant Armfelt Gatchina?
Riksarkivet, Livonica II, vol. 192. Letters from Governor Vellingk 1699-1702