Keep in mind when we design recipes we are estimating while the color described by the brewery is likely lab tested to accuracy for the final product. They may target 13.5 in the recipe but get 20 due to a process issue in the brewery or the malts they are using in house is darker than the grains otherwise available on the market. Either way I would not dispute John Maier's knowledge of the brewery's recipe.
If you're really concerned with the potential for imperfect color then hit the mash with a tiny amount of dehusked carafa.