Service requests, shown as SSR, is a pretty global mechanism across all the main ticketing and dispatch systems (of which Amadeus and the SABRE groups dominate the market) and yes, normally they cross-populate just as things like names and routing codes get interfaced. So it is the 95% plus outcome that a SSR for wheelchairs gets carried over to new bookings. But there is unfortunately the 5% - the interfaces involved were written 40 years ago (or more!) and in irrops corners are sometimes cut by man and machine, so SSR drops out. Hence every so often someone turns up with a disability marker shown on their booking, and may even have a print out of it, but the airport or airline is unaware of it. It partly explains some of the stories of disabled people not able to get off aircraft on arrival, though I strongly suspect that it's more to do with the IT arrangements local to the Assistance Team than GDS/DCS systems.

But the good news is that in terms of the OP's question, if someone is obviously an assistance passenger, and if necessary mentions it, then on BA and every airline I know, they will go to the top of the priority list. The human side here knows what to do, even if the machines lose data. So for example if oversold, these passengers will not be selected for rebooking. And the other factor is that despite the events on Friday, which can fall squarely into the "unprecedented" box, cancellations are rare on BA and other airlines. It's usually well below 1% as you can see from the relevant FAQ thread.