Yes it only work's if you create the file and it would be great to have a criteria to find and highlight custom text cotations.
I also teach and have student's works to correct, so i have developed several methods to detect specific errors.
In the case of custom dimensions I use the "Find and replace text" command in expert mode to replace custom text dimensions with a large text easy to see. The command also let me know the number of such custom dimensions.
Be careful at the replacing steps (step 3 and next) as I experimented ArchiCad crashing if not respecting exactly the steps sequence .
ArchiCad 3.43 to 26