Major Depressive Disorder (MDD), and Social Anxiety Disorder (SAD) or General Anxiety Disorder (GAD), and several other disorders that are related to substance abuse are listed as the most common comorbidities for PTSD. In fact, there is a lot of symptom overlap between PTSD and MDD.
That's probably why VAC clusters them together. And, once a finding is made that you do indeed suffer from one of the 'cluster' they may not need to add another one.
The important part comes in the percentage of the Disability Award that they are going to provide. You need to be brutally honest to yourself about how it has impacted on your daily life. I've dealt with a lot of folks who are reluctant, or even too embarrassed to put onto paper just how bad it is. That means VAC will only use whatever info they get from your clinician to make their decision (and many folks don't give them the whole story either). So, if you can't bring yourself to go shopping, or get on a bus, mention it. Can't perform sexually, mention it. Can't be in the room with a screaming baby without the urge to puke and run, mention it. Repeatedly planned on ending your life, mention it, and then reach out for help. All of these things roll up into the big picture VAC uses to assess you as 'X'% Disabled.
If you need help, the folks at VAC will assist you, and each Legion Branch is supposed to have a Services Officer who can help you in dealing with VAC.