I'm looking for information as to when production of a specific coin is closed. I know that each coin is limited (I think to 150,000) but thus far, many of the coins have not come near the maximum production numbers. I'd like to know when production closes. For example, the Effigy Mounds Monument is the first coin in 2017. Frederick Douglass is the second and is now available. Did Effigy Mounds close production when Frederick Douglass became available? Or does it remain open to further production throughout 2017? Or is it open indefinitely subject only to the the mint's discretion and to the statutory maximum set by Congress? Thanks in advance.