@Kjotleik: As far as I remember:
MADE_DEMAND_RECENT memory is increased when a human civ asks an AI civ for a gift or demands tribute.
So long as the AI civ has MADE_DEMAND_RECENT memory about a human civ, it dismisses demands and pleas from that human out of hand.
MADE_DEMAND is only increased when a human civ makes a demand, and results in a permanent relations penalty ("you made an arrogant demand"). The penalty is permanent only because the BtS LeaderHead XML file doesn't have a (positive) MemoryDecay value for MADE_DEMAND.
STOPPED_TRADING_RECENT and STOPPED_TRADING are both increased when a (human or AI) civ agrees to stop trading with an AI civ. So long as an AI civ has STOPPED_TRADING_RECENT memory about another civ, it refuses to talk to that other civ. STOPPED_TRADING memory results in the "you stopped trading with us" relations penalty.
Both pairs can be used in CIV4LeaderHeadInfos.xml to set MemoryDecay and MemoryAttitudePercent values.
Could be done – but the original idea appears to be that the "recent" memory types decay faster and result in special AI behavior, while the non-recent memory types are responsible for the relations penalty. (Although there is unused game text "You
recently made an arrogant demand!" and "You
recently stopped trading with us!".)
What happens if I set both?
They're treated independently from each other i.e. decay independently and their relations penalties stack. For example (in BtS), as far as I'm aware, the "stopped trading with us" penalty can randomly disappear through decay before the AI becomes willing to talk.
Will all RECENT-values disappear even if I don't set a MemoryDecay vaule for a MemoryAttitudePercent?
No, without a decay value, they should become permanent.
If you need to be certain about these things, you could search the CvGameCoreDLL source code for "_RECENT" to see any special treatment of those memory types and for "NUM_MEMORY_TYPES" to see how memory types are treated in general.
Have you tried the SDK mod that reveals hidden attitudes in the diplomacy screen? [...]
Diplo effects of all AI memory types should be displayed already by BtS.