Well, party chats have two sides to them. There is the party line where people have been chatting in it for hours, or whatever, and then there's the party line called by your favorite name which you form every time you log on.
If you create it as the first person I dont think there should be a history of its chat from last night. Not worth admin's time to backup party lines that aren't static lines.
I'm all for keeping the history of a party line thats already active and simply deleting the history once there are no members to the party line.