Brett,
I agree that there is a need for a reference on this subject. My collection has been largely geared toward that end. I have made a point of collecting type pieces, photos and postcards that would expand the knowledge of the subject.
I have spilled the beans on some of my "discoveries" through the various forums that I participate in, but I have kept certain information back in order to have some new material for a proposed book.
Most information on the regulation insignia worn on the uniforms of the WWI German army is well known. But as you say, this information is not well documented (at least in English) or assembled. To date, nothing has been written about the construction of these pieces and there is no photo reference to use for comparison and identification purposes.
I'm 62 years old and though I have been collecting information for decades, I hope to get down to some serious business when I retire. Right now, I am busier than I have ever been in my work, so it will be a while yet before I have the time to devote to it.
In the meantime, there may be some others that will scoop me and I have heard that there is such a book in the works by a German collector, but I still think when the time comes I will have something of interest to offer. Beside my collection, I will have access to the collections of many friends in the hobby and some of the largest shoulder strap collections in the States. It will be a collaborative effort, as it will have to be in order to cover such a varied subject.
Best regards,
Chip