Welcome to the forum, Morning!
Wow - 20 years of dealing with PTSD is definitely a long time. If you apply for Social Security Disability, keep in mind that you are allowed to work a certain amount and thus earn a little money. I do not know the details of how much or how your pension will affect your qualifying, but I hope it goes well. It sounds to me like you definitely deserve the help.
Have you always had the disability with recognizing faces or is it something that came on with the PTSD? I guess there are other options as well, such as recognizing it when you recognized the PTSD? There is a neurological disorder called Prosopagnosia, which has recently been recently quite a bit of attention because it is much more common than originally. Several universities are conducting research on it and we are learning a lot about it. I recently also watched a documentary on the issue.
Whether or not you, or any others who have responded, actually have Prosopagnosia or the difficulty recognizing faces is related to the PTSD doesn't actually matter. My therapist explained that the frontal lobe shuts down in stress situations and only the back parts of the brain fire. Researchers have discovered this through fMRI studies.
Regardless what the original cause of the difficulty is, I suspect that you can find all kinds of assistive strategies or coping strategies in addition to the ones that you already use that might help if you look up what people with Prosopagnosia use.
Best of luck on your journey!