I don't really know what they are, I just know that London in Victoria's late middle-age was quite different socially from London in the Regency, and that's got to have an effect. It doesn't help that Carriger has 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, so there's a paucity of specific things to point at and say "I don't think that's right."

The one specific thing I had in mind, which is probably not the most significant thing I could have noticed, was a scene where one of the young ladies in the novel says that the social event she's just been to falls short of the assemblies at Almack's. The latter are an obligatory activity for young ladies in Regency Romances, but had very much fallen in prestige by the time of the novel and, depending on when exactly it is set (which Carriger is careful not to pin down) may have ceased entirely. The version of Almack's the young lady describes is one that hasn't existed since before she was born.

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.