Its a re-creation of the detailed model Conan Doyle had either in mind or in his notes. Which as you point out is supported strongly by the fact that a coherent model can be made from the stories
Were any notes supporting a detailed model ever found?
Most authors that write long running stories or sequels keep notes of some sort to avoid contradicting themselves, given the length of the Sherlock Holmes run I would be more surprised if such notes were not used, that would be an amazing feat of memory.
I have trouble envisioning the room next door in great detail, for instance, I know there is a chest of drawers there, but I couldn't tell you if it has 5 or 6 drawers even though I've seen it a hundred times.
You find this a very common factor in many writers; particularly ye-olde ones (where keeping and searching notes was not as easy as now) whereby they would have a detailed and vivid scene in their mind - which was easier to remember.