Agreed Wayne, no two alike.
As fare as the sprocket carrier stampings on #97, if the "5" "18" were May 18, then #97 would not have received that part until at least that date. Given 97 was very likely assembled not long after the completed assembly of #1, kind of hard to imagine the rest of 97 sat around until mid-May wiating for assembly.
The "C" is another confunding stamping.. ?
"5" "18" is from vin 1553.....
OOPS.... misread. my bad. this stamping does make sense for being May 18.
I'd agree w/ Steven V on those marks. They do look like they were made in a rotational line; as Steven suggests, from a jumped chain. Lucky the cases were not broken...