My understanding that, after that point, the hardware drivers could lie and say they've written it and we'd never know, correct?

And even after that, the hardware could return a "written OK" value but not actually do the job, right?

So the point is that without complete transparency from end-to-end, there's no way to tell.

Is that correct?

Yes, and there's also the problem that magnetization of material isn't permanent so your data may disappear after N days even if it were written correctly (typically, N > 5000). Should your "complete transparency" model also include expected longevity of the written bits?