This is always a great question. It is sometimes difficult to explain. If you have seen one come right out of the attic, it is a no brainer. I think you can do a search on the forum here and find a few good examples.
There are many variables that one must not forget also. The vast majority of the G/43's may have never made it much farther than a rail car out of the factory, or to a delivery point, and never really issued. Therefore, we find many examples that look like a dried out piece of playwood, that was made by "Bucky beaver"...with 70 years of dirt on it, and maybe some handling marks from grubby hands over the years. This is what all G/K43 collectors really want to see. granted, a lot of the g43 stocks were pretty well done to.
Now, lets say one made it into the field and was used. I am sure any soldier would not want to have a blonde, raw wood looking stock in the field (most g/k43 stocks were not stained). What did the soldier do to reduce this stock from being seen 100's of yards away (or just not being seen as the FNG)...did he put oil on it, dirt on it, grease...we may never really know.
Then we have the situation where a GI brings a rifle home, and it is so nasty looking (which many G43's are
), they want to make it pretty for hunting ( why most were brought back I would think). Anything can be seen here, sanding them to make them smooth is the #1 issue with a G/K43, then there is varnish, shellac or Poly applied to make them shiny. There can be any range of stock tinkering going on, sanding, buffing, cleaning with harsh chemicals, not so harsh chemical, steel wool, staining, bleaching....and it is almost endless.
It is the collector that has to determine that, by looking at the stock...crisp edges, darkness/dirt in the proofs, sheen to the stock, sanding marks..or lack of sanding marks etc. etc..
Hope this explain a bit better for you.