The chart you have referenced is the "visual shorthand" for a more extensive listing, and the confusion you note is rampant. If you want to go really nuts, the numbering system for the trucks is really difficult.
The answer to your question might be:
- the Jota's are in series, as you note.
- the next is the Omicron, and a desire to make anew.
- then the Ro, which is followed by the RoMB (military) RORO and finally 3RO. And then... the Esaro.
- Following that comes the Esatau, Esadelta, Esagamma.....
- there is of course the late 6RoM (militare)
Now doesn't it all make sense?
Geoff