How to define A, B, C, D stock condition of iPhones and other mobile phones?

I'm trying to define accurately the condition of my iPhone, and I have heard that they are defined by A stock, B stock, C stock and D stock, but can't find a clear description of each condition.

Also, I'm trying to define PGL (Power up, good LCD), and PBL (Power up, bad LCD), but can't find a definition on these either.

Anyone have a good source for these condition grades and how to accurately define them?

I believe its similar to refurbished items.

Grade A - All complete, as new.little to no damage at all on item. Good be an "Ex-Display model"

Grade B - Some Accessories may be missing, a few minor marks but doesn't affect the performance or the use of the item.

Grade C - Item shows its use/age, mostly works but may have one or two faults.

Never heard of any worse than C but I'd imagine that D would be "For parts or not working". Where I work Class D would be listed as "SCRAP! DO NOT PICK"

As for the screens they are pretty much as they say.

PGL = Means the device powers up and the screen display is working correctly, with uniform lighting and no damage or screen burn in.

PBL = Device powers up but the screen is majorly damaged which can affect its intended purpose somewhat.

In terms of conditions, a PBL item I would class as a Class D item, as explained above. PGL can be in either A, B or C.

I don't have a source for you to read but I do work for an electrical retailer which also stocks refurbished and ex-rental electrical items and these are what the terms generally are.

A = brand new, never used, sealed box.
B = used, not refurbished. Likely a demo unit. "Open box" in the store, has all the packaging and accessories. May be used as a replacement when someone brings in a D-stock item. C-Stock will be used for this purpose first, if available.
C = used, looks like it was used, works properly, may not come with all the packaging/accessories that were originally in the box when new. May be used as a replacement when someone brings in a D-stock item. If not available, then B-Stock might be used.
D = Defective, broken. Returned for repair/replacement; needs repair/refurb work.

PGL (Power up, good LCD) and PBL (Power up, bad LCD) are fairly self explanatory. When the unit is powered up, the screen displays correctly - or not. This is only one - of several - tests that are done to see if a particular piece is operational - or not.