The first edition of Aftermath (1980) was produced by Phoenix Games. The few of these early Phoenix sets that I’ve seen have Fantasy Games Unlimited stickers over the PG company logo.
The lid art is different from the FGU sets that would follow: The man is drawn slightly differently, and the woman is missing. The contents are identical to the later (1981) edition.
I’ve seen plenty of examples of an alternate 1981 version with white-covered books (as opposed to the more usual yellow covers).
Later appears a combined Paperback edition, a reprint of the the classic FGU set.
Aftermath! Roleplaying Game
1980, 1981 … Robert Charrette & Paul Hume … Phoenix Games / Fantasy Games Unlimited (FGU) 4000
EDIT May 24, 2020