Brik, get to studying those iron books. Term paper is due soon. Hopefully you will learn more than you did in college.
"Made in USA" almost always denotes a piece made c.1960 or later. Griswold did not mark any pieces that way nor did Wagner before they and Griswold joined up in 1957. That plett pan was made in the Wagner foundry-don't know the exact date but probably later 1960's.
Small TM Griswold pieces are (always?) marked with ERIE, PA and not with ERIE or ERIE, PA. USA. There may be a few exceptions however but can't think of any now. What about the small TM breakfast skillet? The toy No.0 skillet has the large TM, by the way, and it is smaller than the small TM. It's the design, style, etc. of the TM that determine which it is. The small TM doesn't vary (with an exception or two-square toy skillet for one- while the large TM does vary in size and somewhat in proportion.
Steve