Can't help you much. Can only offer a few bits of information and a couple of opinions. Do not know if they were a legal entity.
In my first attached scan I have one of Rockford Silver Plate's ads from 1904. They make it clear they don't sell to department stores. Back then department stores were new and small retailers viewed them in much the same way retailers of today view Walmart. Maybe the Crown Guild was just a trademark of theirs. It's in keeping with their marketing strategy of only selling to small concerns.
The second scan is an ad from 1902 that shows the Rockford Silver Plate Company had branch offices in New York and San Francisco. This disputes what you may have read about them selling only to the Mid-west states.
One last piece of information that might help you on your research. Michael Freeman was the superintendent of the Racine Silver Plate Company when the plant burned on May 5, 1882. He went to Rockford and continued as superintendent. Before he became superintendent in Racine Wisconson he lived in Aurora Illinois for a few years.