That's a very good point — although, as you pointed out, it is easy to miss.
So:
1.0 — Golden Age
1.1 — Superboy
2.0 — Silver Age
2.1 — Multiverse
2.2 — Bronze Age
3.0 — post-Crisis
3.1 — rolling reboots
3.2 — Zero Hour
3.3 — Hypertime
3.4 — more rolling reboots
3.5 — Crisis Cycle
4.0 — New 52
4.1 — Convergence
4.2/5.0 — Rebirth
Oh: I think a case could be made that there were some rolling reboots in the Bronze Age period. IIRC, the term “retcon” entered comic book fandom initially due to the ongoing background changes that were being featured in the Earth 2 comics, as they struggled to cope with their origins being firmly rooted in WWⅡ while their present quickly distanced itself from there.