I've written a number of articles that discuss marks such as "EP" and "EPNS" on silver pieces indicating that this means the pieces are made of silver plate. Here's a comprehensive discussion: What does 'EPNS' mean on my silver pieces?
I'm afraid that my efforts have caused confusion in a few cases where the letters, "EP", appear on a piece but the piece is NOT made of silver plate. This situation can occur when the manufacturer has used "EP" or some variation thereof as the manufacturer mark. Here are some manufacturers where this has occurred:
- Edward Pear (American)
- Elias Pelletreau (American)
- Edward Putman (American)
- Edward Power (Irish)
- Edward Pairpoint (British)
Also, the mark "EPL" was used by Edward P. Lescare (American). Some of the marks included a period after one or more letters, e.g. "E.P". This list probably is not complete; these are the easy examples to find.
It's possible that some of these manufacturers did make silver plate pieces but it's more likely that they made sterling or coin silver pieces.
Here's a helpful article if you need to know more about silver plate construction: Sterling vs. silver plate.