You write that if the middle version number changes it can break a save.
But the version history for 0.2.0 specifically only states it's updated for 0.14.
Will it in this case break a save that already uses Factorissimo on 0.13, if I update game to 0.14 and mod to 0.2.*?

I do understand that you need to break compatibility at some points or you would be very limited in how you can progress with the mod development.
Just wondering in this specific case, as I can't see anything in Version History that would cause any problems.

The only thing that changed from 1.9 to 2.0 is the required Factorio version number. Compatibility is completely preserved.

Ok Thanx, so then I can update to 0.14 on my current map :)

So if I understand it correctly no earlier than Factorissimo 0.3.0 should it break a save now?

Yes. Whoops, I haven't updated the description text. Thanks for reminding me!