To clarify something for Geza in case it was not clear in reading through the catalog or the discussion here ...
Lower case letters after a number indicate varieties of the main number, as in: 599, the basic type I coil. 599b, the carmine-lake variety of this same type I coil. (So the uppercased B of the "599B" in the thread title is technically a non-existent catalog number.)
Upper case letters after a number indicate a whole new stamp ID. If the numbering sequences were perfect, these would have been given a whole number, but often times they are not discovered until too late. They are given the upper case letter suffix to shoehorn them into the logical place. Thus ... 599A, the type II engraving, which might have been called "600" in a perfect world and all the rest of the numbers coming later incremented by 1, etc. Since your stamp is not type II, it might be easiest to ignore much of the discussion here on type II.
The red line on a rotary coil is a common, natural occurrence. Please go back an re-read my description of how these occur.
A gentle piece of advice, the carmine-lake varieties of all of these red stamps in this era are scarce to rare. While your enthusiasm to learn about these is very admirable, the odds of any collector discovering one in an accumulation are quite long, especially someone with a modest number of examples to pick through, including myself. Been struck by lightning lately? Secondly, images of subtle color/shade differences just don't work well electronically. Continuing to try to differentiate subtle color differences via your computer is (quite frankly) a waste of your time. You need to see the two examples side by side and in-person. I would label the stamps as a common, normal line pair of Scott 599 and move on to other areas.
I have identified around 7500 U.S. stamps so far, around 2000 different SC#'s mostly used, just starting new MNH ones. And he had more foreign stamps than US. Many Complete MNH from Nazi WWII germany. I am not sure how much more I will do, just don't think I will have the time once spring time hits. Who would I contact if I wanted to auction off my inheiretance? I am in Massachusetts
Geza - Probably the closest auction firm for you would be Kelleher in Danbury CT. That being said they will want a consignment with a retail value of $500 or more. If all of your stamps are common, you may be looking at pennies per stamp. Ebay may be your best bet.