The sticker on the bottom of the notebook is not burnt or discolored due to excessive heat. The black or dark gray mark in the sticker is normal.
The right side of your Certificate of Authenticity (COA) sticker contains a transparent porthole with individual paper fibers visible around the inside edge. Interwoven vertically through this porthole is a metallic thread with well defined letters that read "GENUINE."
The dark mark you see is the color of the notebook case showing through the transparent portion of the sticker.