recipient semantic

Hi all,

I am a newbie for P3P. After reading the P3P specification, I have one question below:

About <Recipient> element, to be able to select some values e.g. <delivery>, <same> and <other-recipient>, the original service provider must know the data practices of other legal entities so that it can say whether the data practice is the same or different. 
Do I understand correctly? If yes, is there any automatic comparison mechanism specified? 

thank you very much,

Sand