Those are nasty chemicals to use and hard to obtain.
In restoring cars I have found that heat works better than the chemicals. Applying heat then rubbing the area with oil will sometimes expose the numbers.
Sometimes just spraying with carb cleaner (similar chemicals) will expose
the numbers. I will then photo the numbers and reverse the image (negative) to show the numbers. Using the chemicals in the listed porcedure would be a last ditch effort.
Plus most vehicles have an alternate VIN stamped in the frame or body besides the VIN sticker on the door frame and the VIN placard on the dashboard.