Somewhere in the 80's or 90's the nickel die seems to have changed. Not the same change as the late nickels that have laser sharp details making it almost hard to find an example without steps.

When did the changes happen in the earlier nickels?

I read somewhere about changes from high to low relief then another snippet about the end of a series where it remains unknown if any coins were minted that had steps, I'm thinking that was 70's-ish while my eyes are still pretty certain significant changes also took place late 80's or early 90's.

Nickel information isn't easy to find and the redirect from Wexler's site isn't too a site chock full of similar presentations and information.

At least that was my skimming thru kinda precursory impression that may have resulted in my overlooking or missing lots.