Episode #1.7 - S1-E7
Factual error: Mrs. Patmore has cataract surgery, which corrects her vision. Cataract surgery was performed in those days, but intraocular lenses did not exist until 1949, so the surgery simply removed the lens of the eye without replacement, leaving the patient with unfocused vision. As a result, the person had to wear thick "coke bottle" glasses to see.
Answer: Word gets around. The staff are gossips amongst themselves, but those loyal to the family know who to keep secrets from and who they can trust to share in the knowledge.
Phixius ★