Maybe not the 70s, but until the late 60s there was no ABC station in my area. (We actually had public, or as it was then called educational television, several years before we had ABC here.) The CBS and NBC stations here "divvied up" a number of ABC shows between them, using kinescopes or 16mm prints sent thru the mail, and running about two weeks delayed and in odd time slots. As they were only secondary ABC affiliates, a lot of shows, especially daytime, were left out.
The NBC station took 5 of ABC's Saturday morning cartoons and ran them Mon-Fri late afternoons, tacked on to the local "Bozo the Clown" show; (it allowed "Bozo" time to get out of his costume and makeup to do the weather on the early news!), the CBS sometimes ran 5 ABC prime-time dramas Mon-Fri after the late news (opposite Johnny Carson.) Some ABC comedies and variety shows (Ozzie & Harriet, Hollywood Palace, etc.) were slotted into weekend afternoons if there were no live sports events. I recall little if any promotion of ABC shows; they were pretty much regarded as filler.
For that reason, this area was not a particularly fat market for syndicated shows, though I do remember a few (Highway Patrol, Huckleberry Hound, Sea Hunt, Woody Woodpecker, Championship Bowling, and reruns of The Life of Riley and My Little Margie.)