The 1887/6 overdate variety is popular both as an error and as the only issue from that year within the Proof Three Cent Nickel Series. It is assumed that there were left over dies from the previous year that were reused. There are actually two varieties for this overdate, one of which is strong and the other, weak (describing how easily the six is seen). The weak overdate is scarce with the strong overdate significantly rarer and more desirable.