Just my two cents - I don’t think it makes sense to separate Spaghetti Westerns by eras. It’s not really productive, since all sorts of different styles are spread throughout the genre’s lifespan. There’s no single, consistent style tied to any particular period, except for the pre-Leone films, which were basically just American Westerns (and just as bland as the American ones, too).
I’d say there are several key sub-subgenres within the Spaghetti Western subgenre:
1. The Fistful of Dollars likes - A Fistful of Dollars, Django, Day of Anger
2. Revenge Spaghettis - For a Few Dollars More, The Great Silence, Death Rides a Horse, Navajo Joe, etc.
3. War Spaghettis - The Good, the Bad and the Ugly, The Mercenary, A Bullet for the General, etc.
4. Playful Spaghettis (not quite serious, but not full comedies either - Spaghetti Westerns are known for their playfulness in general, but these films focus on that aspect almost exclusively) – Sartana films, Sabata films, etc.
5. Miscellaneous Spaghettis with unique concepts - The Big Gundown, Keoma, Once Upon a Time in the West. (This is the largest subgenre in terms of the number of films, but also the least consistent in quality.)
6. Comedy Spaghettis - They Call Me Trinity, Trinity Is Still My Name, Compañeros, My Name Is Nobody, etc.