I think it depends on the person and where they are with their trauma. Some time ago I got them all the time. But as I use some of the coping skills I have been taught more and more I seem to do a better job at managing the effects of my trauma such that my flashbacks are minimal in comparison to where i started. That does not mean i don't have periods where I get them more. I do, in fact right now I am, but it's because my therapy has touched on some items in my trauma.
I suspect I will having more flashbacks in about 10 months, when I go to them camp where I was first abused. Its a fun camp now, turning a bad memory into a good one is part of it. The other is confronting the past as the past, but doing it in the present. But I am already getting flashbacks from it.