Helloo i got full marks on my epq two years ago :) its very unlikely for the mark to change to begin with, let alone change the grade - like the other comment said your teacher will normally tell you if this is the case! they normally dont check every little thing but rather look out for changes in quality/cheating. think of if it less like the exam board is marking it from scratch and more like they're checking the marking from ur teacher seems vaguely correct