"Overdiagnosing" of PTSD can be occur in a few different ways. For example, we (soldiers) get briefings all the time about the distinction between Post Traumatic Stress Disorder (PTSD) and Traumatic Brain Injury (TBI).
They share several similar symptoms, however they differ greatly in their method of sustainment and long-term effects. TBI is more physiological damage, sustained commonly from impacts and blasts, which are common in combat operations with the Infantry and Special Operations communities. PTSD, on the other hand is more psychological damage.
Because both can likely be incurred from the same incident, it makes it difficult to distinguish between the two. In recent wars, there was potential for TBI to be misdiagnosed as PTSD.
Using questionnaires, 59% [of respondents with TBI] fulfilled criteria for PTSD on the Posttraumatic Diagnostic Scale and 44% on the Impact of Events Scale, whereas using the
structured interview (Clinician Administered PTSD Scale) only 3% were
‘cases’. This discrepancy may arise from confusions between effects of PTSD and
traumatic brain injury.
The US military, in response, conducts frequent assessments before and after combat tours to track any developments in the psychological or physiological damage. However, due to inadequate screening, it is difficult to tell the exact number of misdiagnosed cases.
Statistics compiled by the VA show that more than 83,000 Iraq and Afghanistan veterans have sought care for psychological disorders. The department does not track the number of TBI cases [...] The Defense Department also does not have figures on the number of brain injuries, but Pentagon officials estimated that they have found about 2,500 potential cases so far.
"The number of people who have suffered from mild traumatic brain injury could be in the thousands, but we just won't know about it unless we screen everybody who comes back [...] Maybe it's politics, maybe it's negligence, maybe it's incompetence," Rieckhoff said. "I don't know. I just know that it's taking too long to take things like brain injury seriously."
There are also been issues with malingering which also might account for overdiagnosing. Getting diagnosed with PTSD before getting discharged from the military is a sure way to get free medical disability. I have witnessed several first-hand accounts of this, but those aren't acceptable sources for this website. However, these concerns aren't isolated:
As disability awards for PTSD have grown nearly fivefold over the past 13 years, so have concerns that many veterans might be exaggerating or lying to win benefits. Moering, a former Marine, estimates that roughly half of the veterans he evaluates for the disorder exaggerate or fabricate symptoms. [...] Frueh and other critics of the disability system have sparred in medical journals with senior VA mental-health officials, who argue that the extent of malingering is impossible to know without more research.