Tue Aug 03, 2021 8:33 pm  
History of the development of Greyhawk products

A good write-up of the products and the history of when TSR/WotC/Hasbro provided products for Greyhawk can be found here:

https://rpgmusings.com/2021/08/the-4-eras-of-the-world-of-greyhawk/
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Richard Di Ioia (aka Longetalos)