If the two controllers are sending a message to two different targets, the one sending the lower target address always "wins" arbitration in the address stage. Since the two controllers may send messages to the same target address, and addresses sometimes refer to multiple targets, arbitration must sometimes continue into the data stages.
If the two controllers are sending a message to two different targets the one sending the lower target address always "wins" arbitration in the address stage. Since the two controllers may send messages to the same target address and addresses sometimes refer to multiple targets arbitration must sometimes continue into the data stages.