Actually it went:

0.12.7 -> 1.0.0 -> 1.0.1 -> 1.0.2 -> 1.0.3 -> 1.0.4 -> 1.1.0 -> 1.2.0 -> 1.3.0 -> 1.4.1 -> 1.4.2 -> 1.4.3 -> 1.5.0 -> 1.5.1 -> 1.6.0 -> 1.6.1 -> 1.6.2 -> 1.6.3 -> 1.6.4 -> 1.7.1 -> 1.8.1 -> 1.8.2 -> 1.8.3 -> 1.8.4 -> 2.0.0 -> 2.0.1 -> 2.0.2 -> 2.1.0 -> 2.2.0 -> 2.2.1 -> 2.3.0 -> 2.3.1 -> 2.3.2 -> 2.3.3 -> 2.3.4 -> 2.4.0 -> 2.5.0 -> 3.0.0 -> 3.1.0 -> 3.2.0 -> 3.3.0 -> 4.0.0

You just weren't paying attention.

Technically Node 4 is io.js 4 after Node 0.12 was merged into io.js 3.

So it's really 0.11.x -> 1.x -> 2.x -> 3.x -> 4.0.0. Except that 1.x, 2.x and 3.x weren't called "Node" at the time because Joyent owns the trademark and went on to release their own 0.x release(s) until the merge happened.

just follow the timeline of io.js