Strictly speaking I suppose that you should carry a chart which is CURRENT for the area in which you are operating. Even the latest chart might not be current and several recent issues have come out with obvious mistakes. Again strictly speaking, you should be regularly marking your chart with the latest amendments. This could keep an old chart legally usable. Obviously changes to controlled airspace are the most likely traps and, unless the change is a boundary change, these can usually be entered on your current chart.