Apparently, Buddy Holly and The Crickets were backing up Buddy Knox on this record. It was recorded in Seattle while Buddy Knox and The Crickets were on the 1957 Biggest Show of Stars Autumn Edition tour. Given that both acts were managed and recorded under Norman Petty, it would make sense, especially given that The Crickets (Buddy Holly included) often backed up other acts at Norman's studio during recordings.
Everyday/Peggy Sue was pressed at both the main Decca plants, Gloversville, NY, and Richmond, IN. This is not the only Coral single credited to Buddy Holly pressed on shellac. I'm Gonna Love You Too/Listen To Me has also been confirmed to exist, which was released later than Everyday/Peggy Sue. This is even less common than Everday/Peggy Sue. https://www.discogs.com/release/4047917-Buddy-Holly-Im-Gonna-Love-You-Too-Listen-To-Me-