The listing, Mint error. One number missing. 198? has ended.
Grease mixed with metal dust can form a hardened concretion that will completely clog a die in a particular area. Occasionally, a clog of this type in a letter or number will dislodge and land on the next planchet to be struck. The clog is then pressed into the newly struck coin, forming a impression of that letter/number. This is known as a dropped letter error and is a desirable error. You can barely see it looks like a # 5