Hi @cosign_swim,
I can confirm that this is tray mounted.
In answer to your first question, my best guess it that, since this board is mass produced, different combinations of components are used across a number of different models.
In the case of the AR87, it appears that there are embedded LEDs only on the PCB’s left and right edges. However, I bet another model uses LEDs across the entire PCB. If I get a better idea when I desolder the switches in a couple weeks, I’ll let you know!