The first edition of Aftermath (1980) was produced by Phoenix Games. Most of these sets that I’ve seen have Fantasy Games Unlimited stickers over the PG logo.
The lid art is different from the FGU sets that would follow (1981): The man is drawn slightly differently, and the woman is missing. The contents are identical to the later edition.
EDIT May 24, 2020
See also: CITY STATE: A drop-in Chicago Sourcebook for your T2000 campaign
Early print of Aftermath! Magic!
Gamma World colored map
Omega War: Science Fantasy Adventure Game (1983)