I've been picking up 9mm range brass for upwards of 30 years, never once bothered to trim any of it , loaded 10's of thousands of rounds of it, all with range or my own once fired brass with nary a problem. I'm sure many people will tell you I probably should've, but at this point if any issues haven't occurred, I'm not about to start. In my experience, straight walled pistol cases don't tend to grow like bottle necked cases do.