Oh boy ...
If we or anyone knew the answer to that question, it would solve an interminable amount of arguing.
The short answer is that no one knows.
The slightly longer answer is that floor mats were an issue in some cases, and a mechanically "sticking" accelerator pedal may have been an issue in some other cases, but there are still an ample number of situations out there for which "sudden unintended acceleration" reports exist, but floor mats weren't an issue and the vehicles weren't equipped with the particular accelerator pedal sensor under recall.
A certain Professor Gilbert claimed to have found a situation in which the pedal sensor could be bypassed to cause a situation that looks to the car's computer like full-throttle acceleration, but Toyota hired an engineering firm which has pretty much showed that the circumstances created by the professor were all but impossible to occur accidentally in the real world. Keep in mind that you can deliberately and intentionally circumvent ANYthing if you have the right tools and experience.
That there are some sub-optimal situations in some or all of the involved vehicles, is known. Toyota has not been using an accelerator/brake interlock circuit that would override accelerator input if someone stepped on the brake. But, motor vehicle safety standards require no such system, so this is not a "non-compliance". The European manufacturers have been doing this because one of them has already had their round of "sudden acceleration" issues many years ago.
The push-button keyless engine start is a problem, because it's not readily apparent how to switch the engine off while moving.
But, there is a big elephant in the room that, for some reason, nobody wants to mention: operator error!
People stepping on the wrong pedal is every bit as much of an issue now, as it was in the late 1980's when this was a big issue the last time.
And, every single one of these "sudden acceleration" situations, even if they actually did happen and weren't the figment of someone's overactive imagination, could be stopped in its tracks by shifting the transmission to neutral.
My car has an instant engine disengagement device that is totally mechanical/hydraulic and not reliant on any software. It is called a "clutch pedal". Sadly, not too many Americans seem to know how to use one.