Suppose Albus and Bartleby both have Luck scores of 18. They both have a bonus of +3 on luck-relevant rolls.
Suppose Albus, a wizard, rolls a 27 on Table 1-2; now his Luck bonus applies to Corruption rolls.
His friend Bartleby, also a wizard, does not roll a 27 and thus his Luck bonus does not apply to Corruption rolls.
Then the players look at page 35, which says: "A wizard’s Luck modifier applies to all rolls for corruption (see page 97) and mercurial magic (see page 95)."
Does this mean that Albus has a +6 on Corruption rolls and Bartleby has a +3 on Corruption rolls?
I would think that you would. The Luck chart has a note at the bottom that specifically mentions crits and fumbles working that way. I don't see why you'd treat this differently.