Speculation…Somewhat unsubstantiated theory follows, based on Sound and Silence, p. 32.
Marsco’s original artificial intelligence, the Central Trinity system, was a double-edged gift from humanity to help guide (or regulate, or slow, or limit) the growth of technology in Sol. It was a gatekeeper, and a cultural clock. And very early in its history (“about 50 years into MarsCo’s post-earth history”) it disappears from the public record.
Later on, or possibly at the same time, SenTri becomes the guiding artificial intelligence for ASR, and becomes a control unit for Marsco/ASR, not a cultural ball and chain. What happened?
Theory: ASR happened. The corporate masters of artificial intelligence broke away from MarsCo, and in secret were able to develop a powerful and innovative AI. Using this tool, they launched a strike at MarsCo’s technological heart, co-opting/disabling/stealing Big M’s primary computer and replacing it with one of their own making. ASR isn’t compromised by being under the control of MarsCo’s AI: MarsCo’s AI is a weapon created by ASR to take power away from humanity and weaken their most powerful resource.
Reference: Suggested by Marsco “Sentry” entry, Sound and Silence
Date Notes: Based on emergence of ASR as subsidiary