I would like to point out that errors in husbandry does NOT equal a bad owner. Or one that isn't dedicated.
Many people do not realize that husbandry isn't ideal, because their animals do fine and they don't know better. Or they been told wrong.
Sometimes it just depends on the animal. Some do ok with less then perfect, others do not.
If you have a snake that ALWAYS has rough sheds and NEVER eats really well, husbandry is simply the first thing to double check.
If husbandry was spot on, and no new animals were brought in recently and there were no other obvious symptoms of URI or neurological, then it may have simply been an animal that was never really healthy, and it is just one of those things..
The fact that you seek answers, through a necropsy as well as here on this forum, shows that you are a caring and dedicated owner. We all continue to learn, reaching out is the first step. If you are willing to look into possibly husbandry related issues, post your setup, temps, and how you control and check it all.
Again, sorry for your loss, you had that baby for a while and its always difficult when they pass away, even more so when one doesn't know "why"..
edited to say, I wrote and posted before seeing the last update..