When John uses the word veg tan does he mean vegetable tanned leather ? That describes the tanning process but not the grade. Does he use Corrected-grain leather ? Corrected-grain leather is any leather that has had an artificial grain applied to its surface., usualy not the best leather.
This is not entirely correct.
Vegetable tanned leather, often called saddle leather in layman's terms, does not vary in strength from full grain or corrected grain.
Full grain means that the grain side, where the hair was, has not been altered. This means that all the "character" of the skin as it came from the cow, since we are talking mostly about cowhide, is visible. This includes insect bites that developed scars, scratches from barbed wire, sometimes brands, etc... This is regarded as the highest grade of leather only because like wood the prettiest pieces are desirable and naturally unique.
The next grade is corrected grain which only means that the top layer has been sanded or buffed to the point that the natural markings are gone and the leather is perfectly smooth. This is desired when the goal is to have a smooth surface to work with. The leather is no less strong or good when this is done.
Although you will find much information on the net about leather here are two good places to start.
http://en.wikipedia.org/wiki/Leather
https://www.siegelofca.com/glossary_alph.asp
As I mentioned above leather types and grades and styles are wide and varied. No person can absolutely say that one leather type is the BEST and the rest is inferior because the type of leather used depends on the item it is used for and the WAY it is worked.
In other words you can have a case made with full grain leather that is constructed like crap which will mean that it will likely break down quickly leaving you with a useless collection of full grain leather parts. Or you can have a case made of corrected grain that is well made that will last a lifetime.
Leather is one of the most misunderstood and abused products on Earth. The moniker "real leather" is often used to confer quality of the product when in fact the leather could be the crappiest or the best and the construction could be crappy or great. Just because a product is claimed to be made of leather doesn't really mean anything other than some kind of leather was used, and often in the really misleading cases, not all of the product is actually leather.
Some cue case factories have been discovered by me to make cases that they claim are real leather when actually only the handle covers and the little tag with "real leather" stamped on it are leather and the rest is vinyl which was worked in such a way as to hide the back side of the vinyl.
Anyway, corrected grain only means that the natural markings have been removed and the leather either left smooth or a texture embossed onto the surface. It does not mean lower quality.
This is much different than print leather which is generally a split that has had a surface treatment to add the desired appearance to it, such as crocodile, lizard or ostrich to name the most common ones. Splits come in many many quality levels from super cheap and crappy to fairly expensive depending on exactly how they were made.
We try to buy only the good material and test all of our leather before using it. Any that doesn't pass is returned when we can or thrown away or used for whatever we can find that it can be used for, such as bonding to stiffen exterior leather. We try to use everything that we can if it does not compromise the integrity of the case.
Here is a nice example of a full grain piece that I found with what appeared to be a crude brand on it. I chose this piece for Eric Crisp of Sugartree because he is known for choosing wood with exotic natural patterns for his cues. I figured that he would appreciate it most and he did.