I don't think it would be possible to bring the date back on this coin. Silver is a lot softer than copper and nickel, so any effort to restore the date with any chemicals would just rub it away worse than it is. I do remember reading somewhere that if you take a q-tip dipped in rubbing alcohol and rub as hard as you can, you may be able to clean some of the crud off enough to make the date a little more visible under a bright light.