vanyk

Another thing that many fans do not see is that except official works there are also officially approved works. Official works is everything made by ZUN himself what is considered to be official. Officially approved works are the works that were officially allowed by ZUN to be made (for example works by companies, otherwise they are violating the guideline) and got official licence. The key point here here is that approval is required according to the rules.

Everything else, what is not official or officially approved, are derivative works. They can be made as long they are within the rules. The only complicated part here are official works in which some parts were not made by ZUN (for example art in official manga). These works are official, the parts not by ZUN are also official (if they are considered official (for example most manga in BAiJR is unofficial, but BAiJR is official work)), but as ZUN gives a fair amount of freedom (with some supervision) for creators, the parts which were not specified by ZUN (for example characters' designs and their height) may be considered as officially allowed (so most calculations about heights of characters (and sizes of objects) in manga does not make much sense, I am sorry Lotus Eaters translators).

What are actual difference between officially approved and derivative works? If we will ignore things like financial resources and requirement of approval and we will not place officially approved works higher or lower than derivative works then there are no difference between them. Officially approved works have more resources (because they are made by companies) and they require approval by ZUN, while derivative works do not need this. All officially approved works have licence by ZUN, while derivative works don't need it, but some of them may get licence too (for example if they are published in official magazines).
Official works are separated from officially approved and derivative works.

So not everything that has licence is official, and officially approved ≠ official.

Some Japanese discussion about that (Google translated):