Comment by pentagrama

There actually is a concrete reference for the Windows 95 era research. Microsoft published detailed results from their usability work in the mid-90s, including task based testing with real users, error analysis, and iterative design changes.

Article title: The Windows® 95 User Interface: A Case Study in Usability Engineering (1996)

Link: https://dl.acm.org/doi/fullHtml/10.1145/238386.238611