Dave,
There are some really smart people on this forum that can answer your questions but I'm not one of them. My experience is limited pretty much to what you see in my postings.
I have a copy of the AKAH 1908 catalog reprint and that has pages of German hunting bags. Although 'more modern' versions of the basic bag are in the catalog it doesn't appear that the fundamentals have changed much for many years. That is very useful for ideas and dimensions although I scaled my down a bit. Other info sources were T C Albert's two part article in the 2019 Muzzleloader magazines and this link to some extraordinary work.
https://contemporarymakers.blogspot.com/2016/05/jagdtaschen-game-bags-by-eric-ewing.htmlMarc Hamel made a bag for me several years ago that is inspired by these style bags and the really high quality of the design and workmanship has been inspiration for what I try to do. Having that in hand and being able to study the details has helped keep the aimed for standard high.
Hopefully some of these artists will chime in and point anyone with an interest to other sources of information.
Dennis