I brought this up at an early stage of the discussion, but not in such details as you did.
I also mentioned the fact that if the Crystal was overtaking and approaching the Fitz from abaft the beam (112.5 degr. relative) he would be seeing only the stern lantern of the Fitz.
Somebody also mentioned that US Navy vessels have two sets of navigation lights (or two settings) one being the regulation strength per SOLAS requirement, the other a dimmed version for operations where they wanted to be inconspicuous, but not "running dark".
Somebody also mentioned that warships shows very few if any lights, other than nav lights at night.
So with a low radar profile, low lighting, + that there were no AIS to identify any weak blip on the radar screen, or a single white light in a field of lights from other ships, from fishing boats and even from close by shoreline, There were also a moon rising at the time, which could also make it hard to see a gray warship, designed and operated with the aim to be as invisible as possible and making no efforts to improve that in a busy shipping lane by at least transmitting AIS signature.
With all that in mind it is entirely possible that the OOW on the Crystal could have missed the existence of the Fitz until very close, especially if she was overtaking the Fitz, thus being obliged to avoid the overtaken vessel.
At the same time, the OOD on the Fitz could have assumed that the Crystal would alter course to safely overtake according to the COLREGS, being blissfully unaware of his own invisibility to others.
It still does not explain why the Fitz didn't take last minute actions to avoid a collision, also per COLREGS. With the maneuverability of a Destroyer, I can see no reason, or excuse, for NOT doing so.
The moral of the story??: If you are making effort to hide your identity, existence and operational activity, you should take action to stay clear of all other traffic, or make yourself visible to others and follow the COLREGS