Episode #6.3 - S6-E3
Factual error: During the wedding the groom and ushers are wearing boutonnieres pinned to their labels. Pinning boutonnieres to your lapel is a very new method. Traditionally the flower goes through the lapel button hole. This would still be a common use for the button hole at the time.
Episode #3.3 - S3-E3
Other mistake: At the end of this episode after Edith is jilted at the altar, Albert makes some rather "home boy" comments about the food and then asks if there is any cheese to eat as if that's all he's used to or wants. This seems inconsistent since for the rest of the series Albert is the guy who seems to appreciate well-made food and wants to be a cook.
Episode #5.6 - S5-E6
Continuity mistake: When Lady Mary is competing in the Point-to-Point horse race, she is riding her mount sidesaddle style, wearing a long-skirted riding habit. When she (actually the stunt rider) jumps a hedge, she is now riding astride, with both legs over the horse and using a two-stirrup saddle. Also regular riding breeches (pants) are underneath the long skirt when it flies up a bit. These would never be worn with this type of lady's riding habit.
Episode #4.1 - S4-E1
Other mistake: They act as if Carson's friend Charlie has his first appearance in season 4 episode 1, but in an earlier season and episode he arrived at Downton Abbey and caused a scene in the library trying to extort money.
Episode #1.3 - S1-E3
Factual error: The Turkish character "Kemal Pamuk" is given the surname "Pamuk." However, surnames weren't used in Turkey till mid-thirties. Yes, Pamuk is a real Turkish surname but no Turk would be using surnames in 1912.
Continuity mistake: Every letter's handwriting looks the same - no matter who wrote it.
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: Lord Sinderby purchased the house, furnished and appointed, from someone else, complete with staff that come with the home (some of whom aren't happy to be working for a Jewish family). He bought the title, as well. If the artwork featuring Jesus is valuable, he might keep it. Also interesting, his ancestors Anglicized their name, though he is proudly Jewish.
Michael Albert