Nike seems to have a huge stock, either it is an error or they really do have 40 pairs of the trainers in stock lol. I just added and released 40 pairs for fun to my cart.
Nike has a restock on those multi trainers and black trainers.
http://store.nike.com/us/en_us/pd/flyknit-trainer-unisex-running-shoe/pid-582107/pgid-582109?cp=usns_aff_080113_je6NUbpObpQ&site=je6NUbpObpQ-d5sFHVQw8MH.bBxwNkgP4g
go nuts
B-Grades are just cosmetic defects. They are a hit or miss. I believe someone said, they label B-Grades in batches. So if they make a batch of 20 Flyknit Trainers, and say 3-4 out of them are cosmetically flawed they label the whole batch B-Grades. Can someone else confirm?
In my experience...
With patience and mad research, copping for retail and below can be done. Although I did cop a few B-Grades, they are flawless.
Volt Trainer $199.99
Unpadded Black Trainer B-Grade $83
Volt Racer B-Grade $135
Orange Racer B-Grade $127
Multi Racer $162
Greyscale $127
Multi Lunar 1 $100...
They have some B-Grade Volt Trainers on Ebay Size 11 and up for $200-250, with quadruple ebay bucks right now get like 16 dollars back.
item number: 390860982017
yellowing is just an ongoing chemical reaction between the sole and oxygen. aka moisture (H2O), humidity can affect that. Air has about 20% oxygen as well. I figure exposure to moisture and humidity are the main differences between that guys pair and yours.