Sharp corners for zipped pouches

I loved going through my stash of Japanese cottons and 'Ink and Spindle' screen printed fabrics to choose the ones made into these zipped pouches.

Why so many? They're an order for my friend who will sell them in her shop,  'Bay of Apostles'  in Apollo Bay, Victoria. Very exciting!
One of the techniques I've used for making the sharp corners is a method called 'wrapped corners' invented by the well known American sewing instructor, Nancy Zieman. This technique is explained in her book 'Sewing A to Z'.

There's no need for trimming and once turned right way out, just like magic, you have a sharp and square corner . Nancy Zieman also uses this method when making corners on collars. I can see it being used any time you would normally do the 'pivot and turn' method of sewing corners.