Source: www.buttonmuseum.orgBusy Beaver Button Museum. License: All Rights Reserved.
A button featuring Charles Schulz’s Snoopy character, manufactured by Butterfly Originals Ltd in Cherry Hill, New Jersey. As seen at the Busy Beaver Button Museum.
The 1958 copyright date presumably refers to the Snoopy character and not the button’s design, since the typeface it features (Bullion) wasn’t released until 1970.
Peanuts merchandise is always difficult to date, since the copyright listed is always for the characters, not for the item itself.