The versions of Mavic 840 and MAVIC 841 shown are the familiar versions, with a conventional allen key hanger bolt and dropout adjuster.
However, the version of the MAVIC 845 shown is one that I have never seen in the flesh. It attaches to the dropout hanger using an allen key screwed in from the inside and has an extravantly shaped pulley cage - using a design typical of Simplex. And, indeed, all three derailleurs were manufactured by Simplex.
I have seen this dropout attachment system on an early Mavic 840, but never on a MAVIC 845, perhaps one day I will.