A few years back I found one of my Gold Tip's from theprevious season, which was my 'lucky arrow', while I was out shed hunting. Iinspected it and used it again for several more seasons of hunting. That arrow and had gone thru at least a half dozen deer. Unfortunately one yearone bigger bucks I've shot took it close behind a shoulder and snapped it in half.
I'dexpect it would take several years of exposure to direct sun, water, or acidic soil to compromise the integrity of a quality carbon shaft to the point of making it unsafe to shoot, but that is just my personal guesstimate.
In any case, the effects of weather on a shaftis a very good question to consider. I'm sure for liability reasons any arrowmanufacturer would have to recommend discarding it. Considering the price of a single arrow, it's really probably not worth risking it.