Where To Land DMX Input On A 4 Port DMX PCB

Symptom

I am unsure which port to land DMX input on my custom distribution's DMX Interface PCB. The factory-wired DMX out is landed only on port 4. 

Part number on the PCB is: 7099B4601A

Description/Explanation of Issue

It is important to note that a 4 port DMX PCB contains headers for both DMX A and DMX B. The board is divided in half horizontally as shown below: 

If there is only one factory wired DMX Out then the opposite DMX Out and In are considered spare ports.