Ummm... you do know there are scans for BPD and other personality disorders? Science for mental health pretty much is non-existent, beyond contradicting studies - one saying x - the next contradicting and saying y. If you want to call contradicting studies science, then sure, you could do that if it floats your boat. Personality disorders are difficult to study due to the emotional reactivity associated with them, but they can still measure givens in them.
According to science, you could apparently measure PTSD. Well... they were wrong, because you can't, as another study proved due to inaccuracies between assessment and measurement. Actually, there are quite a few who claimed you could measure it, to only find many inaccuracies. They can measure neuronal and synaptic aspects via MEG and other methods, though the science is still out on factual aspects of PTSD. Very new stuff, basically... as it is for personality disorders and every other mental health disorder.
Mental health is anything but scientific, and the above was purely discussion. There is more knowledge surrounding personality disorders, regardless the name you choose from the list, than most other disorders. Sure, PTSD has been around forever, thousands of years... no doubt personality disorders have as well. Neither were simply known and people used to just kill the mentally ill, or call them crazy, and be done with it. PTSD is one of the most studied over the last decade, no question... because the media created that one.
Mental health, nearly as a whole, is best guess. Science... now that lay in medicine, no question... but is only just starting to creep into mental health, and lacks dearly in PTSD. There is no such thing as CPTSD. Even those confused with Chronic PTSD, the actual diagnosis is PTSD with chronic symptoms.
Because of the above, best guess aspect of mental health, science is only JUST starting to appear in order to make anything a little more factual / physically proven and factual for all mental health diagnoses... but they're all a long way away. The research into personality disorders, from a scientific based view, is showing some good results from last view. Again, there is no CPTSD and PTSD is still best guess, as science is doing more damage than good in studying PTSD at present. Well... actually they're going around in circles, is a better description.
They don't understand the biology of PTSD... so I'm unsure why you're claiming that. Read the studies, and then research the opposite, and you will find them too. I cited personality disorders have some science behind them... CPTSD has none obviously, as it doesn't exist, and PTSD they just keep pissing in the wind with science and biology. They have near zero biological foundation for PTSD to date, because they don't even know what the hell it is, how it forms or exactly where it forms in the brain. Why one gets it and another exposed to the same event doesn't, so forth. The experts have no idea about it... all best guess.
This isn't a new issue with people reading studies... in that you read them as though they're factual and have some meaning. Do you read the biology ones that their results are in rats, not humans? Do you do what most do, and take only what they choose and discard the contradictions?
If you're reading old posts of mine, and claiming contradicting information... then just ask me now, present tense, because things change since time of writing a lot of stuff on this site.