Pedantry? actually that's the kind of error which seriously irritates me in period dramas.
It's on a par with one I saw set in the 1890's, where you got a quick glimpse of a satellite dish on the side of someone's house. Forgotten what it was called.
Or the continuity errors where an actor is talking to someone, and after the reply when the camera moves back to him, he's wearing a different tie.
Then (being interested in trains), I saw one film from the 1950's which showed a train about to leave, and after the camera panned back to the locomotive after a romantic goodbye, same class of loco, but with a different number.
Oh and not forgetting the film apparently set in December, where you can see fake snow falling outside the window. Then when they shoot outside, all the trees are in full leaf, and the shadows cast by the actors, very short - and it's not "6 months later". Oh and when they come in from the snow, the flakes just stay intact on their coats, instead of rapidly melting which they would in real life.
...and don't get me started on fake lightning, always cast as directly overhead, so the thunder is immediate....
OK call me a sad but observant pedant if you like.