In the United States, lawyers often name their businesses The Law Offices of So-and-so, in the plural, even when they are solo practitioners, working out of what would be regarded as just a single office, according to the criteria that govern the use of office in other contexts.
Admittedly, in some cases, the lawyer may have an assistant, whose workspace is in a physically separate room, but that hardly seems to justify the plural in the name of the firm. As lawyers are subject to the rules of professional responsibility that prevent them from stretching the truth in promoting themselves (in the ways that may be tolerated in other businesses), it is hard to believe that the use of the plural in these cases would be as widely accepted if it were just a shameless lie.
So, is there something in the history of the word office that could, even arguably, justify the use of the plural in these cases?