Definitely 1974-S. 100% sure, no doubt.
1. This is not a proof coin, so it cannot be 1975-1979. ONLY proof coins were minted in San Francisco those years.
2. The mintmark style on this coin was only used for ONE year on business strike coins. 1974.
3. This is the same style mintmark used through 1979 on proof coins.
4. All 1970-1973S business strike coins had a smaller, less blocky and 'filled-in' mintmark. Easily distinguishable as different.