I'm just going through a diagnostic process with my psychiatrist at the moment but the way I see it diagnostic categories in psychiatry have a tendency to confuse cause and effect and it's useful to bear that in mind. For example 'depression' is a symptom that can be caused by many things - including PTSD and BPD but also endogenous conditions like stroke and also of course reactions to things like bereavements. So a diagnosis of depression doesn't necessarily tell you anything about aetiology, it tells you what you are experiencing but in itself is not enough, the underlying causes still need to be worked out and treated. On the other hand C-PTSD is a diagnosis that focuses more on aetiology - it is based in a pattern of complex deeply ingrained internalised traumatic experience that is harder than PTSD to resolve into single discrete events due to it becoming part of a person's life experience for a protracted period during their development and bound up with disorganised attachments and internalised self-systems. This can cause many symptoms including some that have traditionally been seen as clustering around 'personality disorder' related traits, others include depersonalisation and dissociation (which is a coping strategy and a strategy for constructing a viable self-system in the face of external threats), and of course also effects on mood and anxiety, and sometimes also psychotic symptoms. So I don't personally see it as an umbrella term but more an underlying set of life experiences that can result in multiple patterns of symptoms and that many of these can be confused with or overlap with traditional concepts of clinical conditions.