This all dates from a time when we were fighting a war and most of this type of information was "secret" and even if it was not secret, due to the mind set about security, it was not well known or general knowledge. Although we now have a new government, most of this stuff was developed to kill them & their friends so it is now an embarrassing situation, & still the info has not all come out.
Now that you have the background, what I am writing here cannot be accepted as fact, only as what has been pieced together.
WA = Walter Annex or plant. Another plant was attached to PMP's original plant in Pretoria West, on the same site. Not just another production line, a whole plant. Named after Allen Walter an ex-employee at PMP who developed the Walter process, which cut down the number of draw stages needed to produce a case. I think the plant was named in his honour, but all plants used his process, not just this one, it was just named after him.
LA = Luther Annex or plant. Where the Walter plant was primarily for military production, the Luther plant was more for commercial ammo production, but they did make military ammo when there was a need. Fanie Luther was the chap it was named after, also an ex-employee at PMP. Fanie is an abbreviation of Stefanus. Again, this plant did not do anything special that he developed, only named after him.
Hope this helps