I think a lot of people who were gluten intolerant back then did not know what was wrong with them and they certainly weren't going to be discussing openly their bowel movements. At our age, it's a topic for discussion among good friends at times without much embarassment, but teens and early 20s? Not unless you wanted to be the "butt" of many jokes!
My friend's husband is gluten intolerant and didn't know what was wrong with him. He developed the gluten sensitivity as he got older and it got worse in his late 40s (he is mid 50s now). He likes to go running, and one of his daughters noticed he came home regularly without socks on, knowing full well that he had them on when he left the house. When he told her what happened to the socks as he was jogging in that rather secluded path in the woods of the park, she was obviously disgusted and said, "Dad, you need to go see a doctor!" And that's when he was diagnosed by an MD. He has no loose issues these days since going gluten free and everything is quite solid, if you get my drift.