When Identifying an L-500 from the Bill Lawrence Pickups (Classic) period, you should be aware that the L-500 product line underwent name changes throughout 1981, The hot L-500L was renamed the L-500XL with the cleaner L-510L becoming the new L-500L. the L-500R did not change in output or name.
Only Bill Lawrence Pickups (Classic) pickups featured a curved blade, others are flat. I am looking for info on when this change was made (I'm guessing somewhere mid to late 1983, not long after the "Bill Lawrence USA" imprint appeared). Current By Bill Lawrence (WS) pickups feature wider blades than current Bill Lawrence Products (EZ) pickups.
This is an example of a By Bill Lawrence (WS) electric guitar pickup (right). These electric guitar pickups do not feature "Bill Lawrence USA" markings anywhere on the pickup.
The marking "Bill Lawrence USA" (see pic left and right) in the plastic housing is found on Bill Lawrence Pickups (Classic) and Bill Lawrence Products (EZ) pickups. This marking appeared on pickups in the last month of '82 or early in '83.