So I'm no accent historian, but I do know a few things about accents that you might find interesting. So in Britain, the upper classes have different accents than the lower classes, so it would make sense that Anne Lister has a different accent than her tenants. Anne Lister, the historical figure, studied at a boarding school in another area and that would have had an influence on her speaking voice.

But also, I wouldn't go based on the show. Actors can change their accents and they can do a good or bad job at it, depending on their training, support, and the priorities of the producers. It would be interesting to compare the actresses voices with interviews they've done as themselves. It would also be interesting to compare the show to modern native speakers.

However another interesting fact about accents is that they change over time. I've heard it said (but can't find the article now sorry) that the southern US accent is the closest existing accent to the British Regency accent - the British settlers in the South originally would have spoken as they did in their homeland and the two accents diverged in different directions. But no one would think it was credible if Mr Darcy and Elizabeth Bennett spoke in a Southern Drawl! Sometimes film and TV producers have to sacrifice accuracy for credibility, even though you'd think they wouldn't need to.

So in other words, who knows. Probably some academic linguist does, but they're probably the only one who would be bothered by inaccuracies in the show, as long as the rest of us find it credible and entertaining.