S designation on Parker Guns

[Jim Thynne]

I have a 12 ga Parker that is listed in the serial number book as a S.
It made me wonder if this designation means something more than just a error in the original book.
the rib is marked;
MADE TO ORDER FOR THO'S RUSSELL
PARKER BROS MAKERS MERIDEN CONN. VULCAN STEEL
It looks like any other V H Parker with the exception of the rib, which clearly was done at the factory.
The serial number is 176575, and has no special features other than the rib markings. It made me wonder if there was a designation for "S" Special orders on Parker guns that was so noted in the books......" Food for thought!"