>wired in at least four separate
>stages, each added without decommissioning its predecessor.

The house we lived in when I was a teenager was an old Victorian terrace and had been wired in multiple stages in apparently vertical strips - kitchen and bathroom first, then lounge and master bedroom, then the servant's rooms (presumably after they stopped being such) and finally the remaining bedrooms, dining room, and utility room.

Our neighbours still had a functional electronic bell system as well, which was parallel to the other electrical installations (ours sadly had had the bells removed probably 50 years earlier).