If you are able to get the exact coordinates of the corners and go to the coordinates via any application it will not be exact. This is an intended error that changes periodically so that bad people don't use it to fly bombs and such remote control.
Now, knowing that you can figure out the correction by going to a known point and getting the coordinates and use that correction to locaty the other points.
There are also servers the post the correction every day for surveyors. If you look long and hard on the www you can find them, Easier to use the first method I mentioned.
Keep in mind the x, y, z coordinates will all have different corrections.