On the obverse where it is missing lettering, and some flattening on the rim could be from a file, and cause the loss of weight.
Wow.. So much going on with your Cent. There is also a split planchet possibility . Struck after split? I have to find my list of foreign coins struck at San Francisco mint during different years. Or it could just be PMD
Here's a couple of more images and a new one between LIBERTY and IN too .. I also don't think it's PMD, the coin sits level too, no bends ..
Can you compair it to another cent for diameter. It does look oblong but that could be that its smaller in spots rather than larger in others. The main culprit would not be grease as the rims would not be severally affected. It does have some characteristics of a split before strike but the overall circulation wear and tear has done a good job of confusing what may have been the tell tale signes.
Nearly all of that is from PMD. I do see what looks like a couple die chips at the date and what might be the remnants of a lamination under AMERICA. After all that abuse, it would still only be worth the copper in it.
65 years of circulation is what happened to it. A couple of experts, which includes Tom Delorey (writer and 2009 Numismatist of the year) on the PCGS boards also say PMD.