Some builds require one or the other, or both. Just depends on the footprints used on the PCB and the way the plate was cut. The image below shows a stab cutout for a switch plate that is compatible with both PCB-mount and plate-mount stabs.
The characteristic that identifies it as plate mount compatible is the little notch I have circled in red.
Here is an example of a plate that is only compatible with PCB mounted stabs:
To identify a PCB that is compatible with PCB mounted stabs look for holes like these highlighted in blue:
