Do you mean as opposed to an after sale job done by a local smith?  Assuming the smith does a good job, I guess you would have to have spent some time looking at factory issue ones so as to be able to spot the difference, if any.  I have two 445 shrouds that were factory drilled.  The factory put plug screws in the holes, so that might be a difference.  Of course some one might toss the plug screws when they put mounts on.  Or there might be no plugs if the factory installed a mount.