I agree, they didn't start retconning things right away. What I will say though is that very early on, they started having to manufacture ways to bring in reasonable facsimiles of classic concepts. These were not retcons, they were new versions of old ideas, but to me it was the sign that there were mistakes made in the wholesale changes originally. The need to find a new way to bring in a Supergirl. To find a new way to bring in a General Zod. To find a way for the Legion to have a Superboy on the team. Stuff like that were clear signs to me that they knew early on they screwed up by mandating so much of his classic lore removed, in that very early they created new ways to bring them back while still trying to stay true to said mandates. And virtually all of them paled in comparison to the original concepts.