This video shows you how to make and apply corrective shapes that blend in a neat linear fashion after the Envelope.
Usually shapes are applied before the Bones. Which makes very little sense for correctives and they end up with bizarre-looking uneditable shapes to compensate for the rotational route they will have to take. its very hard to blend them in to look natural because of this odd route.
With this system, you can post-edit the correctives at any time and they look how you'd expect them to look.