Moulding descriptions have a 2-3 letter acronym in their description (eg. LWM, WM, WG) - what do they stand for?
Thanks for clarifying your motivation behind asking. If your goal was to learn a universal nomenclature of moldings, I was bringing bad news:

My 25 years of directly related experience has uncovered no such uniformity. The only way to clearly and universally designate moldings is by function.size, and description of profile. For less common items and large orders, a builder is wise to approve full scale rendering or physical sample. 

Alpha designations for moldings [in my area] are unique to the mill that cut them. If commonality exists beyond that, it goes unnoticed, especially in the field. There are a few numbers that are widely repeated, though I haven't found anyone that knows their origin; even  at the big stores, you'll find "356" and "444" casing.

in a given locale, it's usually understood what is expected to be in a house, and it's reflected in the limited variety of locally available stock. A deviation would simply be specified by its difference, e.g., "flat" casing; "3 bead" screen. As is typical in trade terminology, there will also be some regional variations in common terms. Around here you'd hear "speed base" to refer to the contractor grade mdf ogee baseboard. 

Overall sizes are pretty standard (though called on both nominally and diminsionally), as are some shapes (though sometimes described instead of named). Basic crown molding are 2⅝", 3⅝", 4⅝", etc." Colonial "(traditional) or *cove" . Typical baseboard is 3½", 4½", 5½", etc "Ogee". Perhaps it's "base with cap".Casings are 2¼", 3¼", 4¼,, and may be called by "flat", "2-step"/"3 step,." Shelf edge", or nosing, is screen mold, "flat", "2-bead", or "3-bead". 

Of course, all of this is period relevant, both in terms of style and nomenclature. Not long ago, "base and case" was interchangeably used to trim "doors and floors". 

Anyone in the business of dealing with these products should be able to communicate through description using basic profile features such as cove, bead, shoulder, flat, thumbnail, etc. Additionally, some shapes have several variations, like the Ogee. They're based on academically recognized architecture styles. 

These are just some examples. Should be  at least as clear as mud! I know it doesn't answer your specific question (as I don't know that it has an answer), hopefully  it is  helpful in some capacity. 

Im always interested to learn the experience of others. Perhaps we might find some evidence of a more universal rsal commonality!