pedanther

Oh yes, Almack's was the first thing that popped into mind for me as well -- along with some major changes in technology, e.g. railways instead of stagecoaches, lack of highwaymen, lack of duels, totally different fashions, much higher value set on religion, the Metropolitan Police, completely different international relations (France ally, Prussia enemy)... That's one thing that Georgette Heyer is so much better at than her Mills & Boon imitators: she knows her social history, knows what the latest gadgets were, knows the popular prejudices and the shifts between eras (there's a big difference between late eighteenth-century and the 1820s, as big as the gulf between the 1920s and the 1950s, not to mention the little matter of a French Revolution in between!) and knows the real people from history who figure in the background of her stories. It's not just chocolate box costume drama.

a tendency to acknowledge the existence of social rules and obstacles only when and so far as they're convenient to the story she wants to tell

Fanfic has a tendency to do that with the constraints of canon, and it always irks me. In effect, the characters end up being able to get away with any amount of handwaving unless and until some element produces useful angst, whereupon it's suddenly a major issue to be hashed over at exhaustive length...
It's like those authors who create 'character flaws' that only ever appear when they want their heroine to be mildly embarrassed in front of the Designated Love Interest and fail to inconvenience her at all at any time when it might cause an actual obstacle to the plot :-(

I don't object in principle to a tropey instead of a historically accurate version of the Regency, or of Victorian London, or of Wodehouse's Edwardian era, but I think the story might have benefitted from picking just one of those and sticking to it.

Ouch :-D

I see the author is American, which never helps... (again, they have a tendency to fetishise the whole 'too, too quaint' concept of British history) :-p
Obviously there are Americans who do write good costume drama, but the average fantasy aspirant does tend to suffer from an additional cultural deaf ear in addition to the usual issue of anachronism.