There may not be all that many "patents" on shingled sleeping bag construction. You can go to http://www.uspto.gov and search the patents for this yourself. The patents are required to divulge the design concept in order to be granted as a patent and receive patent protection.
In general, shingles require more cutting and sewing than do layers. So, there is some more cost, perhaps. The stabalization of the insulation with more sewing could have other disadvantages, such as weight. But, then again, it might not.
At the USPTO site, you may have some problems viewing the illustrations. It seems that so many commercial software firms are so anxious to make their software "your software", you may have browser plug-ins for viewing that are incompatible with the USPTO.
All hail comeptition.