I have read the posts here and was debating saying anything. It sounds like there have been many answers from, Ammo is not like bread, it doesn't go stale to every time you look at your gun you need to change it out. Okay, not so much that last one but close.
I have been in the Public Service business so to speak for the last 25 years +/-. We would shoot our duty ammo once a year to get the fresh, crispy new stuff. In all that time I have never been told the specific reason why other than rotating to the new stuff. I suspect that it has more to do with the bean counters and not having to explain why something didn't go bang or maybe it went bang too much. This and our range instructor found the latest and greatest 1 shot magic bullet that we were all switching to (Thank you FBI).
In all of that 25 years I have used the cheap ole FMJ bullets that the agency can get the cheapest because again, the bean counters didn't want to spend $$$ on the good carry ammo to train with. I have never fully agreed that you need to do lots of practicing with duty ammo so you know what it is like when you shoot it in a real situation. I have been in on a handful of OIS investigations and never once has an officer mentioned something about the difference between training ammo and duty ammo. They were more concentrating on what the HE double tooth picks was happening and even then they didn't recall everything. I have never really understood why people think that they will be able to tell the difference in a real life situation vs training the difference in the ammo they are shooting. I have had 25 years of shooting training ammo and duty ammo and I have never really worried or noticed a big difference.
This and the need to always ask that the best ammo for defense drives me crazy. Practice with what you can. If money is no object, go out and buy carry ammo and practice with it all the time. If you are like the rest of use, get a cheap but good FMJ and practice. Practice is good. Talking about how often to change your ammo or what ammo is the best carry ammo is a waste of time. Not trying to disparage anyone but discussions over what is the best ammo or best gun are exercises in futility. Carry what is comfortable and shoot what you can. I have never heard someone complain with what gun they were shot with or what the ammo was, mostly because they weren't talking.
Just sayin.