For example, most of the authors of the old-time classics were not employed by Microsoft when they wrote their books. I think Charles Petzold (Windows Programming) was a freelancer, Jeffrey Richter (MFC) was working a company called Wintellect, David Solomon (Inside Windows NT) had a seminar company (Solsem), I think initially primarily for VMS and Mark Russinovich (Inside Windows 2000) at Winternals Softwre.