- 1958-1959 - Embossed Bottom Stamp
- 1959 - Embossed Bottom with stylized flame Stamp
- 1960-1961ish - Blurry Blue Ink Stamp (may or may not have Pyroceram printed)
- 1961-1966 - Basic Model Number with stylized flame Stamp (usually black ink)
- 1966-1969 - the Cornflower makes it's appearance in the bottom stamp
- 1969-1972 - "for Range & Microwave" Stamp (with or without small Cornflower)
- 1972-1979 - Hologram Stamp on the bottom (VERY hard to see unless tilted to the right angle in the right light)
- 1979-1985/86 - Block Stamp
- 1985 - 1999 - 2nd Embossed Stamp found under Handle or on the bottom (Block mark was still used on Roasting Pans until 1987)
I hope this helps narrow down the dates of your pieces!