I am quite sure you have access to far more information than I, but specific amounts of medals on a server being gained randomly by players is still a quota...the implication is simply that the quota amount varies on indeterminant factors.

As to what troops sent when attacking valleys and npcs's I simply shared what has consistently given me medals. I hit 200+ lvl 5 npcs daily with no troop loss and zero medal gain. I also hit 50 level 10 npc's daily with 5k archer loss approx and currently have over 700 each of nation and justice medals...I'll keep farming them my way, others can do what they want. There are likely better ways.