I'm no expert for sure, but the two Slant Eries I have, a 5 and a 7 do not have the # on the top of the handle. IIRC they timed out in 1905. A large block # 12 does. They went to about the end of the 1920s I think.
Check ebay listings for Griswold skillets and look at the pix. A little bit of everything on there.