John,
Are both of your shallow skillets iron or are either made of aluminum? 228 is the catalog number of the aluminum No.8 shallow skillet as shown in Griswold Catalog No.45 (c.1915). I am thinking that someone at Griswold grabbed the pattern for the aluminum version one day and made some iron pans with it. I don't know if there would be ANY differences between a pattern for an iron piece and a pattern for an aluminum one.
Pattern number, by the way, for the No.6 milled bottom skillet is also 729. By the time that the milled bottom skillets were first made Griswold had long ago abandoned making the shallow skillets so reused that pattern number; something that they did on quite a few other occasions.
Steve