Was wondering if something like this yellow ink defect would affect the grade of a card. (Above the accent mark on the e)
No one can exactly answer your question because the answer varies from grader to grader. It depends on how the grader feels it affects the appeal of the card, so in that sense yes, it does. However, generally speaking with a stain that small there needs to be something else wrong with the card for it to drop a full point. For instance, if the card was mint in every aspect excepting one speck of whitening, and had 60/40 or better centering on the front, it would have a good chance to pass as Mint 9.
Things like that add up, but don’t necessarily directly effect the grade. Like I said if the grader feels it affects (detracts from) the overal appeal of the card then yes, it does effect the grade. I hope that makes sense.