I didn’t, but I considering the world’s workforce is around 3 1/2 billion people, and that in the developed world, the percentage of office jobs is around or below 50%, however the majority of the world’s work force live in underdeveloped parts of the world, I would estimate the total number of worldwide office workspaces to be significantly below a billion. And - even the number Microsoft themselves claim, appears to be only 1.5 billion total per https://en.wikipedia.org/wiki/Usage_share_of_operating_systems - with this particular quote in the article (emphasis by me):

On 27 January 2016, Paul Thurrott summarized the operating system market, the day after Apple announced “one billion devices”:

Apple’s “active installed base” is now one billion devices. […] Granted, some of those Apple devices were probably sold into the market place years ago. But that 1 billion figure can and should be compared to the numbers Microsoft touts for Windows 10 (200 million, most recently) or Windows more generally (1.5 billion active users, a number that hasn’t moved, magically, in years), and that Google touts for Android (over 1.4 billion, as of September). My understanding of iOS is that the user base was previously thought to be around 800 million strong, and when you factor out Macs and other non-iOS Apple devices, that’s probably about right. But as you can see, there are three big personal computing platforms.

I think it’s fair to say that “billionS” is a bit of an exaggeration - that’s all I meant to point out.