On a note about diseases like scurvy being common modern knowledge but unknown from earlier times, if something isn't a problem then we don't really look into it.
One example i'll bring out was the Roman Fever, basically malaria, they didn't really get malaria very often so no one really cared. As the population of Rome grew they expanded agriculture which needed irrigation. Early Roman irrigation was pretty bad and had a lot of stale water which became breeding ground for malaria carrying mosquitoes.
People still didn't put it together than it was the mosquitoes and microscopic bacteria, they did notice that "miasma" from stale water was likely making people sick, it was a recent change that was linked to the fevers.
So poor people getting sick from scurvy may well be associated with just poor people being poor unless there's something to compare to. If one neighborhood of immigrants liked to ferment cabbage and they were fine from the disease. People would piece the puzzle together.
So the annoying part about the MC coming along and being "oh yeah that is scurvy, eat fruit" is just going to make people dependent on him and not reinforce critical thinking skills. xD