Often, suicides aren't counted because they are passed off as something else, or simply because the person is said to have died by suicide for personal reasons and not for reasons related what they experienced in the forces. Often, too, this will be covered up by saying it was an accidental death. The word “suicide” won't be put in the obituary.
It happens even among us, in the army. One of my colleagues killed himself the day before he returned from Afghanistan, in our lovely chemical toilets, and it was made to look like an accident in Afghanistan, which wasn't the reality. Today, I am still fine, but that's why I said that I would notify the media if I ever decided to do it. It's to demystify this.