Honestly not 100% sure how it is currently calculated. From what I can see based on the UpdateCraftSkill function, it doesn't look quite right.
The chance for the player to skill up from crafting an item from a profession (not considering changes to configs) should be ((GraySkill - PlayerSkill) / (GraySkill - YellowSkill))
.
Vanilla Wow wiki/Wowpedia (both of which cite a Wowhead comment), and an r/woweconomy post, likely got it from the same comment.
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Windows 10 x64