I believe improoer alloy mix lines are a little wider usually or at least aren't as uniform as roller lines usually seem to be. The early 80's copper pennies with roller lines are actually quite common. One of the big giveaway usually, which coop explained is the raised areas, such as the devices are devoid on these lines. If it was truly an alloy issue they would be present no matter how worn the coin is. Because these are actually stains they can be worn off due to circulation. Doesn't mean they are always worn off, but usually.