Good point. Some errors could add value. And on the most common marbles, finding one out of round could possible turn a marble which is worth a nickle into one which is worth $1 or more. A football shaped cateye might possibly be worth more than average. Some people collect egg-shaped marbles and other oddballs. I think mostly for fun, not value. However, you might be able to get money for them if you market them cleverly.