So, as promised, I called Dell Tech Support moments ago, and reported the same test findings to them that I've reported to you. They confirmed the same information you all have been offering: the F12 hardware test is the one they rely on, and the Extended portion of the SupportAssist test has been griped by many others for the same reasons I have complained about - random and spurious test failures from a working laptop. They said they were "working on it", and gave no update date. So, I asked them to add my name to the list of complainants, in case that would help spur an update to SupportAssist.
Are there any other issues I should confront regarding this adventure before I close this thread as Solved?