MBHP CORE V3 & DIN & DOUT boards

I have my MBHP CORE V3, together with 4 DIN and 4 DOUT boards. I am assuming all 8 of these boards will connect to the same port on the MBHP CORE V3 board.  So am I correct in thinking I can use a single y-cable, and connect 4 DIN and 4 DOUT boaards in a cascading fashoin, and connecting the middle of the Y-cable to the CORE.  I intend connecting 128 LED’s and 128 momentary switches to the boards.  What I do not understand is how will I know in which order to place the DIN boards, as well as the DOUT boards, because to me they all look identical.  Am I missing something obvious? The boards were built for me by a friend.  Please advise.

dont matter, the dout or din - line is looped thru the boards…

but i think its better to put the din boards at the beginning of the chain, because they are more sensibel - they are sensing…

Thank you Phatline for this answer.