I am not sure that I agree with Steve M. How often you use the vest really is not that consequential. Just because I might wear the vest only for investigating bumps in the night, the rarity of use does not make the vest okay to use. Whether or not the vest is still good is based on the condition of the fibers. How do you check? You mentioned that a brand name vest that is properly cared for should be okay to use after expiration. How do you determine if it was properly cared for and even it is was, how do you know the fibers have not degraded. I have seen 10 year old vests that look good on the outside of the panels, but appeared to have salt (from sweat) coming out of a small split seam. The panel had been cleaned nicely, but the vest had actually seen a lot of use.
I would not buy a used vest on the word of the salesman that it was worn by a little old lady on her way to church on Sundays, not stored in the trunk of her car, and not allowed to get wet or if it got wet, was dried properly. I don't like to trust people who stand to make a profit when what I am trusting on is on the gamble the vest will safe my life because it is still up to full strength. If you own a vest for more than 5 years and you know how it has been cared for, then you may decide to wear it for another year or two. That is YOUR call.
Whether you wear that vest every day or just when you check bumps in the night. Just because you wear the vest irregularly does not mean that someone will shoot you with an underpowered round that won't penetrate the crumbling fibers inside. The vest has to work right, completely right, on the first time. There is no, "I got shot just a little thought my vest" sort of reasoning here.
Once your vest does get shot, it is shot and needs to be replaced. That being said, don't buy the used police vest that have the one or two little tears or deef scuffs in the panels.
