Dickens saw himself as a sociologist though, so a lot of effusive descriptions are meant to capture a sociological phenomena or a nuance of London culture.

"Having not gone through any intermediate state of change" could tell you a few thing: the owner of the house adheres to an outmoded aesthetic, the owner couldn't afford to upgrade the exterior (maybe a minor aristocratic house in decline), or if the implication is that the knocker skipped a part of a larger change, it probably signifies that the house has been purchased by tasteless merchants and they just painted over an ancient knocker, or that the house has been purchased and remodeled a bunch of times but the knocker is brand new and sticks out.

But yeah he also published in serial format, so he was probably just trying to hit his word count a lot of times.