You likely also know from your research, that the shell (concha) identified you as a pilgrim as you entered a village for the evening. It granted access to pilgrim lodging, albeit primitive by today's standards.
During the way's walk, the shell (concha) was also used to drink water from fuentes and other surface sources.
It was also used to scoop foods like stews and soups from a common cooking pot.
Other uses of the concha include rubbing two of them back-to-back, across the ridges, to create a wood-like musical tone not unlike a maraca. I attended a party in Santiago this past August where this was used as a musical instrument to accompany the very spirited singing...after enough wine was consumed...
The edges of most concha could also be VERY sharp and could be used to cut some things.
This also accounts for WHY the concha was worn in full view, usually in the front, hung about the neck, or fastened to one's hat or staff. You would recognize an approaching pilgrim and tend not to get your staff, sword or knife out to prepare to defend yourself and your companions.
Remember, life on the road in the Middle Ages was a lot like the mythical Zombie Apocalypse... People lived short, hard and brutal lives. They usually died in their 40s or 50s, if they lived that long, typically from maladies that are now preventable or treatable with a pill or injection. A simple sinus infection was mortal. Any puncture would led to sepsis and infection.
Maladies such as we frequently complain about, like achy joints and bones were almost unheard of. Usually people died before the developed diseases commonly regarded today as reserved to the more senior amongst us.
Back in the day, people just struggled to make it from day to day. Being on the road as a pilgrim engendered an entire new and more sketchy groups of concerns.
If you want to better understand how precarious life was for a pilgrim back then, try reading Cormack McCarthy's "On the Road," a post-apocalyptic story of a man and his son walking North to South in the Eastern US to find a place of safety. The time is now, or in the future. But the issues and concerns are strikingly similar to what might have been found during the Middle Ages...it creeped me out.
BTW...The larger the concha, the greater your portion of food or water...so bigger was better.
Also, and just as an FYI, many of the red Cross of St. James stamped, contemporary conchas sold in souvenir shops are sourced from China. They are not individually marked. You would have to see the shipping case they came in.
Sometimes the shells are from China, but the cord is added in Spain. I could tell because the paper the corded shells were packed in was a Spanish newspaper, sometimes from a Coruna. The shells are the same genus and species as those used originally for "Coquille St. Jacques" and other seafood dishes along Basque and Spanish Atlantic coast. Just sayin...
The 'BEST' Conchas, IMHO, are the fresh ones you pick up from the beach yourself, or obtain from a restaurant. BTW, the Pilgrim Office in St. Jean Pied de Port obtains it's non-stamped shells from local restaurants...Coquille St. Jacques...remember...
More FYI, that is where the name of this French seafood delicacy originated "St. James Shells." Colloquially, "coquille" means scallop. Technically, it translates as "shell." But the shape is distinct an unique enough to describe the specific type of mollusk.
I hope this helps.