I think, officially, upgrade availability comes out of the same bucket as award flights (so A). But the possibility of upgrading on the day (especially at the departure airport of the relevant flight) must surely widen availability beyond that?

From your post it sounds as though you live in Germany. For tickets bought in France upgrade to First is not available from D class, only C and J. But D Class can be upgraded on tickets which have bought outside France. Upgrades to First are never available from Z Class.