These are very common from 1982 through 1988. The numbers tend to go down drastically thereafter. Main reason for that is the mintmarks were no longer added to the dies by hand after 1989. Another reason could be the new wash they started using around that same time for the zinc blanks prior to being plated. Speculation more or less, but one thing I can say is that in another 30 years people are really going to wish they had stashed some rolls from the mid 1980s...they are going to be very scarce and very valuable.