[arhiman57]

I guess it's safe to say the Professional IRIS was obsolete and largely forgotten by the time the Hardware Developer Handbook was written...

You're totally right, the rev 1.0 came back in 1994 if I remember correctly. Even earlier, in 1991/1992 (compared to 1996 fro the this old sgi faq...), on comp.sys.Sgi, some question were not answered on nor totally by official  SGI tech support about early Professional Iris spares parts, upgrade path, OS support etc. And you can find many comments "these systems are very old and obsolete right now". So it's definitively not impossible that they make some mistakes  (the fact that a book like that exist is also crazy...)

As you say, the time frame between each upgrade, new series is so short back in 87/88...