Interestingly enough, on a recent LHR-ORD flight, I was MX'd twice in two days. The "substitute" flight number was a 4 digit number, not the typical 959/949 that accompanies scheduled UA LHR-ORD service.
The GE machine did NOT know that I was on flight 9XXX, but rather thought I was on my originally "scheduled" return, so I'm not certain at which point the data is updated. I had to tell it which flight I had actually been on.

Dave