fwiw, i've had a similar case. installed some calipers on a carbon fork. got into a minor accident on that fork. no visible damage but later on when i bought some new calipers, i had a lot of difficulty taking the old caliper out. had to pry the old caliper out of the fork using a flathead screw driver. finally got the old caliper out but the new one won't go in. i thought the two calipers might had used different bolts so i measured with my vernier caliper. the bolts are slightly different but the same recessed nut worked for both, so it probably wasn't due to that. in the end, i think the minor crash might have caused a slight deformation in the alloy crown of my fork. i tried really hard (hard isn't the right word, actually, more like precise) and finally got the new caliper in.