Peggy Knippenburg has two Lodge skillets she got from Grandmother Nellie Schieffelin.  I offered to clean and re-season them as they were as heavy with crud as you could imagine.

From CastIronCollector.com
1940s-1960s¹
– Inset heat ring with 3 notches at 9/12/3 o’clock.
– Molder’s mark incised at 6 o’clock or raised, on a small flat blob of metal above the size number at 12 o’clock.
– Later, letters denoting pan type, e.g. “SK” skillet, “DO” dutch oven
– Lids have grid of pointed tips for basting drippers, size number and diameter or pan capacity incised on underside

After ca. 1960
“Made In USA” added at center