Hi 7/3,
Re. my question of backing, I noticed in the damaged section, as though the print had been folded and the emulsion layer torn, that the hatched effect visible over all the photo is still visible. I assumed that the backing itself was composed of some sort of material rather than paper. Further, the hatched effect is not regular, rather like a cloth type material. I have never seen an old photograph printed on cloth material as a darkroom process. I do not know either if parchment could be used for such process, nor if parchment has such fibers.
Best regards George
Enlarged section of your original: -