That certainly doesn’t sound right. That section is a subheading of Ability Ratings. Ability Ratings is broken up into Exponents and Shade. Its sibling headings include things like Using this Book, Dice, and Voices in my Head. This is foundational text, upon which lies the rest of the work.
Shade doesn’t just describe what to do when rolling; it defines what Shade is in the context of the game, and it does so before describing the rolling procedure. And before even that, it says that every ability number in the game has a shade. I believe that order reflects the nature of the section as a definition.
I think, “Every ability number in burning wheel is accompanied by a letter,” is meant to illustrate that Shade is integral to ability ratings by definition. You don’t have a velocity without a speed and a direction, and you don’t have an ability rating without an Exponent and a Shade. I think this reading is supported by the statement being true outside of the context of rolling dice: Every ability number in Burning Wheel is accompanied by a letter; Shade plays a part any time an ability is factored numerically. At least as far as I know. Again, I’m pretty new. The only example I can think of where this isn’t the case is Superficial Wound (maybe, hence this thread). Stride, maybe, but that is specifically called out as not having a Shade.
Can anyone else think of an example where an ability’s Exponent is called for but its Shade is not?