So, I recently acquired this cool gem that I’ll be scanning at the earliest convenience.
Unfortunately, this document is rather non-technical, but there’s some useful info inside including details on how to use the drivers that would have came with the trackball-equipped Model M5-2 (IBM Enhanced Keyboard with 25mm Trackball for long) mentioned. If I’m not mistaken, this could be a candidate for the earliest reference of this keyboard in documents.
If you’re interested in having scans of it, I’ll post once it’s done. Due to COVID, access to a scanner is a bit of a problem for me right now. There’s few enough pages that I could string a bunch of photos together as a stopgap.