I am going to provide a hypothetical (but commonly encountered) scenario to enunciate this point.
Say a veteran has an extensive history (going back about 15 years) of encountering MANY mental health providers (many doctoral-level) in the VA system and NONE of them have ever diagnosed PTSD or a trauma- or stressor-related disorder. Instead, they diagnose disorders like major depressive disorder, 'anxiety' (not a disorder, I know), substance abuse. Then veteran has an extensive, thorough psychological assessment/ workup (say, by an intern or a provider who knows what they're doing) utilizing such things as structured interview (CAPS-5 or SCID-5), objective psychological testing (MMPI-2-RF, or PAI, or MCMI), extensive interviewing around Criterion A, actually attempting to examine the 'association' (if present) between the putative stressors and current symptoms, examining co-morbid conditions and their association with current symptoms, etc., etc. Takes several sessions, several reports/notes, and a good deal of time and effort. They fail to uphold a diagnosis of PTSD and, instead, rule it out.
Veteran turns around and complains, 'fires' the clinician who ruled out PTSD and another therapist in the same service enters a consult for assessment/treatment for 'therapy.' Then a therapist slaps a PTSD diagnosis (first one for that patient, ever) on the chart (with absolutely NO justification whatsoever...not even a PCL-5...literally just the four letters 'P' 'T' 'S' and 'D' all capitalized and in order. That's the justification for the diagnosis. As a result of that 'diagnosis,' a consult is entered for the PCT (specialty clinic) for treatment of PTSD.
Let's assume that we may be dealing with a (not uncommon) scenario that a patient with non-PTSD psychopathology (substance abuse, personality dysfunction, depression/anxiety/neurosis) has actual psychopathology that needs to be honestly and accurately worked up and treated psychotherapeutically, but said type of patient may be seeking 'an answer' to the question 'WHY?' as in 'why do I get angry and mean and aggressive with people.' Obviously fishing for the collusive lying response from a clinician ('because of your PTSD.'). Parenthetically, if I never heard the phrase 'I had a PTSD episode' as a referent for an episode of emotion dysregulation and inappropriate/aggressive outburst again...that'd be awesome.