That TM was also used on the square skillets 21xx series, the chef's skillets with bakelite handles, many porcelainized casseroles, and probably other pieces. The No.3 is the only regular skillet it was used on and my thoughts are that Griswold may have intended to switch all round skillets to that TM but got bought before they could do it. I'm pretty sure that it is the latest Griswold TM used. I'll have a No.3 square skillet at the convention with the same TM.
Steve