Our (TMDb) use of the word collection can be misleading because for many it is intuitive that this must include any group of related films, be it sequels or an abstract relation such as the link between Three Flavours Cornetto. However, the guidelines are generally simple: the films should be sequels. There are some exceptions, but they do not seem to apply in this case. This means just because a group of films may be considered a trilogy, it does not necessarily follow that they meet the requirements of collection.

Enter lists. I created a Three Flavours Cornetto list when lists were introduced.