I don't know if I still have any of the old Automatic Electric ordering information around. As I remember there were a number of ringer options available when ordering phones. There was straight line (not frequency selective) and frequency selective that would ring at only certain ring frequencies. There were also those with taps as you talk about. Ed could probably remember what that system is called, I would have to look it up.
So with all those options you can see how they can do 8 subscriber party lines.
-Hal
