With the Silver Age era of DC easily divided into the early fun era pioneered by Gardner Fox and John Broome and the later more serious social consciousness era led by Denny O'Neil and Neal Adams, is it possible that the Earth-1 that Flash "returned" to in #179 was really another Earth-1 that became reflected in the other titles by the end of the year, coinciding with DC's new direction?
This sorta reminds me of the "Marvel Time" theory that the Marvel Universe from 1961-1968 shifted reality with the birth of Franklin, which just happened to coincide with Marvel's move towards licensing and realtime ending.