I'm not sure what month the cards were available, but the film was pushed for a much earlier release date in late 1977 than originally planned by Spielberg of early 1978 (due to financial difficulties at Columbia Pictures, and also the want to piggyback off the Star Wars phenomenon).
Topps wanting to have cards distributed along with the initial release may have been a factor to not being able to tie everyone down in time its' cardboard production.
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