yes this is correct. both shift buttons act as 1. its just more convenient to have one either side for user control than have a single shift button in middle of controller.
if they implement separate shift buttons then different new midi messages will need to be written.
however if they gave us a second shift function then the user could add extra modes suited to each persons needs that is not a direct button on the ddj rz. thinking like switching dvs mode from absolute and relative,,, colour Fx parameter 2 control etc... instead I'm using my keyboard short cuts and mouse on the gui