Continuity mistake: Every letter's handwriting looks the same - no matter who wrote it.
Episode #5.7 - S5-E7
Revealing mistake: When Tom and Sibbie are on the bridge dropping sticks into the water, they run to the other side and you can see their movement through the bricks.
Episode #2.4 - S2-E4
Continuity mistake: Mary has written a letter to Matthew. We hear her voice reading the text, which begins: "So there we have it. I look forward to introducing the two of you, just as soon as you are next at home..." Next, when the page of the letter is shown, it reads "...happy to hear - come to pass. I look forward to introducing you to Sir Richard, just as soon as you are next at home." (00:11:03)
Character mistake: At one point they say the gramophone was gift for Sybil's wedding. Later they say don't play the gramophone from Mary's wedding, it will make Edith sad.
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 ★