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The normal 8.38 is just that - normal BBS concave, whereas the mellow mold is a specifically flatter board.
You can contact DLX yourself to check if you want.
Of the fifty plus, yes actually more than fifty of the DLX 8.38 decks I have had pass through my hands, with half of those I skated myself, there have been three that are definitely the Kyle Walker "mellow mold" and all three of those were way flatter than the nomal boards in every way. I still have one, unskated and most likely will never skate it, even though I like mellow, this thing is so flat it is ridiculous.
Comparing it to a box of other DLX 8.38 that it is in with, it is so easy to see the differences, example being the angle of the kicks is only about 15 degrees, normal boards are between 19 and 22, down to about 17 to 18 when flattened to my liking but anything lower than that feels like your foot is just going to fall off the end, if that is any indication for people who like numbers, but if there are still any doubts, I can go take some pics again for show and tell.
If I could also give the mellow mold a number, it would probably be about VIII or IX when compared to the usual I, II, III or IV if that is a different indicator with the press numbers too, so yes being about 8 or 9 is super mellow.