Hi @tyme
The "missing SD" 2-cent coin is more valuable because it is a recognized minting error (a die variety) from the early years of Australian decimal currency, making it rare and highly sought after by collectors. The "SD" stands for Stuart Devlin, the designer of the reverse side (the frilled-neck lizard), and on certain, specific, early issues, these initials were omitted or failed to strike properly.
Here is why this error increases the value:
- Rarity/Scarcity: While millions of 2-cent coins were produced between 1966 and 1992, the "No SD" variety exists only on a small, unknown number of coins from specific years, primarily 1968, but also 1966, 1967, and 1981.
- Key Collector Dates: The 1968 "No SD" coin is considered a "key" to the 1966-91 series because of its low mintage and, when found in high-grade (uncirculated/pristine) condition, it is considered exceptionally rare.
- Error Appeal: In numismatics (coin collecting), errors in manufacturing are generally more valuable than standard, high-mintage coins. The missing initials represent a "puzzling anomaly" in Australian coin history.
- High Demand: The "No SD" 1968 2-cent coin can fetch hundreds or, in very high, independent, or certified, grades (MS66), over a thousand dollars.
I will have to check what years mine are. But since I have had to move into a caravan at my mum's, my coins have gone to a friend's place to be looked after.