Dunno. Haven't had a cock in me yet, but I have ejaculated from prostate stimulation with toys up my ass. I have NOT had an orgasm from it, however, and those experiences are precisely how I learned the difference.
At least the handful of times I accomplished this, it was highly pleasurable to feel (and see!) cum shooting out of my cock, without a doubt. But I remained in the heightened state of pre-orgasm, and hadn't yet achieved that sense of completion and release that comes with even the smallest real orgasm.
Not saying it can't happen. It may be that guys with a lot more anal experience than me may have experienced a full orgasm from anal penetration. But I do have enough experience to know that orgasm and prostate milking are not necessarily the same thing.
My newest story: Midlife Resurgence: Piñas Coladas
Not in the contest but Festively Flashing: Disrobed
Festive Flash competition entry: Amy's Mom
I get dicked by a federal agent in Recommended Read Dick Job
I pork everyone in my other Recommended Read, Pork by Northwest
Card catalog? Hard catalog! My library