Wayne,
To clarify this, firstly, my full comment is necessary: "I flag designs that apply a lock washer directly to the PCB."  

A flat washer between the lock washer and PCB is recommended as lock washers tend to tear up the PCB as the copper pad, if present, is generally only 2 maybe 3 mils thick and tends to get torn to varying degrees roughly proportional to the type of lock washer and the applied torque.  And, if there is no pad, the lock washer often tears the FR4.
The other reason for wanting a flat washer is to more evenly distribute the torque load as lock washers, especially split lock washer apply a high percentage of the load to the split.

I am old school, but my preferred stack-up from PCB surface out is FLAT (washer)- LOCK (washer)- NUT.  If using SEMS, then this stackup is FLAT (washer)- LOCK (washer)- SCREW (head).