1974 S Cent W/ A Strange Mint Mark

I'm not seeing what you think you are seeing "under the mm." Can you send us the link to the reference site that shows what you're referring to, please?

The S/S is a south. Note the bottom loop on the lower loop and on the upper loop on the center. There were two different mintmark punch locations for that die. On your coin, there is Machine Doubling present on the date in the same direction. So the machine caused the affected are on both the date and the mintmark. On a RPM, the punching only affects the mintmark area. Most of the time you see Machine Doubling affecting the date and mintmark in the same directions.

On this coin, you can see the metal striation lines on the affected Machine Doubling on both the date and the mintmark.

The punching of the mintmark area is a separate step on the pre-1990 coins. So if the Machine Doubling on the date and mintmark are in the same direction it is Machine Doubling. This also applies to doubled dies as well:

Note the date is showing a DDO, but the mintmark is showing Machine Doubling with only the date showing a DDO, and the mintmark only showing Machine Doubling. (the mintmark is not affected by the variety, but by the Machine Doubling)

CoopHome: If I see Machine Doubling on the date and the mint mark, what does that mean? it was caused by the machine.

I try to help everyone see, what I see on a coin. Sometimes, my explanations hit the target. So when a return question is asked, I try to explain it a different way. (I often try to make the explanation different as my thinking adjust to new information I discover, I update them) So I'm not offended by a second question to clarify something. (I view it as a challenge, to make it even more clear)