The first "coded" letter from Olof Sandberg to Samuel Barck is dated Lund 25 November 1717. Lennart Thanner appears to have considered the code as an attempt to cover the presumably sensitive content. This appears very unlikely as it would probably have taken a contemporary reader only a few seconds to figure out the meaning. It seems more likely that Sandberg tried to amuse Barck.
Sandberg starts out by saying that the knight "Sankt Jörgen" (Goertz) appears to have lost favour with the King. He then mentions "Pehr Speleman i Gårdarijke" (the Czar), who in Sandberg's opinion has bitten off more than he can chew. Sandberg then goes on to say God bless "Far" (the King) as things will then go well for "ungefar och ungemor" (Frederick of Hesse and Ulrika Eleonora). If "far" dies they will inherit the farm, which has fared poorly lately. They will have to spend time on repairs etc. Pretty standard stuff and certainly not a code that would have been of any use if the intent was to keep the content secret.
Source: Riksarkivet, Ericsbergsarkivet, Autografsamlingen, Vol. 182