My interpretation on it is this: if you buy into the chemical imbalance theory, AD's that target the chemical differences in the early trauma brain (serotonin 1b deficiency as opposed to other serotonin receptors) you will then be augmenting the levels of the correct serotonin receptors, thus providing relief for the specific types of depression and anxiety to early trauma.
Anecdotally, I am on an off label dose of an antipsychotic, at first for my depression, anxiety & insomnia, and now just for insomnia because I have had adverse reactions to traditional antidepressants, which were then labelled as being on the bipolar spectrum.
If there had been a more tailored antidepressant that had hit the right serotonin receptors for me, then I may potentially not have had these reactions, and my treatment would have followed a more efficient course.
I may have gotten that entirely wrong and oversimplified it, but that is how it read to me:).