Stan,
Why couldn't Mephisto put a dye on every seed they grow in a year. Dye every seed the same color, and switch out colors year to year. It wouldn't have to be a dark color, a very light tint is all you would need. This way you could easily see the year of birth just by looking at it. If you kept a light color, anyone trying to re-color a seed would find they wouldn't be able to match the color exactly, and it should be obvious. You know, they coat carrot seeds and such, with a fertilizer coating that is colored.
Maybe something you guys could experiment with, if you thought it would help.