My interest is pursuing a personal hypothesis that the myth of the so-called Nazi soap” may have actually had a factual industrial size basis, not as bars of household soap, but as a type of industrial liquid soap used in the emulsion polymerization process vital to production of synthetic rubber and that German secrecy, deception, and destruction of records, combined with mis-interpretation of surviving record fragments, have led to this potential industrial scale use of corpses being overlooked.
Your point regarding glycerine being of far greater strategic value than domestic soap is valid, but when synthetic rubber production is brought into the equation I feel glycerine may become closer to equal.
At this distance in time I think looking for “smoking gun” records of actual Nazi soap making would be counter productive.
Diligent but perhaps narrowly focussed research seems to have yielded records of every trainload of humans to Auschwitz and other concentration/death camps.
However, I seek records of goods which were transported away from the areas of the camps.
My particular interest is the Auschwitz area including the I G Farben “Buna” complex also known variously as I G Farben Monowitz, I G Farben Dwory, I G Farben Auschwitz. (In this context the word buna originated from the abbreviation of butadiene and natrium, the process by which an early type of synthetic rubber was created, but buna appears to have quickly become a common use term for all types of synthetic rubber)
Conflicting records appear to exist regarding the production purpose, capability and status of I G Farben Auschwitz.
Also of interest would be reliable records relating to strategic fat reserves, overall synthetic rubber production and movements of workers/slaves to Auschwitz 3, AKA Monowitz slave labour camp, AKA Buna camp.
I concede that the association of “Buna” and the Auschwitz area may be part of an elaborate deception aimed at hiding the true purpose of the I G Farben complex.