Another commenter answered that, at least in regards to medical equipment (similarly, embedded systems code for an ultrasound machine, in 1989) -- once code is

Another commenter answered that, at least in regards to medical equipment (similarly, embedded systems code for an ultrasound machine, in 1989) -- once code is FDA-approved, people won't touch it. I imagine if the F18 software met some milspec requirement, a similar rule would apply.