Diagnosis was made with the ICD-10. Therefore it isn't accounting for the population that could have a diagnosis of Complex Trauma (CPTSD). This diagnosis wasn't added to the ICD-11 until 2018.

In contrast to regular PTSD, that is caused by a single terrible event (acute), CPTSD is the trauma that people develop by living a series of negative events (chronic). The events don't need to be terrible, but they can be.

This study draws an association between poverty and traditional mental health issues. However, I wonder if in many of those cases the trauma of struggling to cope with poverty and other associated issues might be causing CPTSD as a 'gateway' mental health issue (undiagnosed) that sometimes leads to depression, anxiety and other traditional mental health issues. Anyway, if this is true, those suffering only from CPTSD are not only being underserved, but they could receive intervention before they develop major problems. https://en.wikipedia.org/wiki/Complex_post-traumatic_stress_disorder