Afaik it's like this:
Situation: all enemy provinces conquered by several allies.
If the temporary leader of an alliance (i.e. the alliance-member that declared war or was declared war upon by the enemy) holds the enemy capital and annexes the enemy, each alliance member will get the provinces he owns.
If the temp leader doesn't hold the capital and makes peace, he might get something from it, the rest get nothing.
If an alliance member, not being the temp leader, can annex and does so, everybody gets his share (not sure about this one).
If such a party cannot annex and makes peace, it's a separate peace and the war continues.
greetings, Oranje
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Common sense is the set of prejudices acquired at age eighteen.
Albert Einstein