Aktie-Bal IV (1997) (DOS)
You're wrong — not a trilogy, but a tetralogy. There were four "Aktie-bal" games released for DOS.
Aktie-Bal IV is not considered canon anymore. It was actually a reskinned version of the original Info Harry, during the time when Info Harry itself wasn't officially available anymore (from 1997 till 2006). Same thing applies to Kerker III, which was a reskinned version of The Geddies during that same time period.