The door unlock can be pretty much anywhere and we have at least 10 different locations in our fleet, at least one of them where it is directly adjacent to the rudder trim. Added to that there are some very bad CCTV setups around as well, for example having the screen on the aft overhead panel behind the left seat. An FO would have to lean out of his seat over the center pedestal to see anything on that, identify the person who wants to enter the flightdeck, keep observing the area why he supposedly opens the door. In that position he would neither see the flight controls and displays nor the door unlock button or rudder trim.
Still, both knops have a different design, but the mode of operation is the same.
Newer CCTV setups display the picture on the lower DU, much more convenient.
Boeing approved retrofits or even boeing designs can be ergonomic nightmares, and the whole door thing is just that in some configurations.