A little history. ‘Canon’ originally referred to ecclesiastically-approved texts that were included in the Bible, as opposed to the Apocrypha, that was left out. The term later came to mean any collection of works with a privileged status - Shakespeare’s plays and poetry are part of the canon of English literature, for instance. A joke about German scholarship led in 1912 to the concept of ‘canon’ being applied to the Sherlock Holmes stories. By the end of the twentieth century, ‘canon’ came to mean the official interpretation of any collection of artworks.
‘Fanon’ refers to similar shared interpretations that do not originate in the artworks themselves, but are agreed interpretative practices among fans, or even just among singular fans (what is sometimes called 'headcanon'). Some things, however never appear in the artworks directly, and thus cannot be strictly canonical, but still have an origin outside the fan community. For Star Trek: The Next Generation this is especially so of certain class names assigned behind-the-scenes to starships, which were given by the show’s technical gurus, Rick Sternbach and Michael Okuda. Such terminology is what I call supra-fanonical; it goes ‘above’ the fanon without reaching ‘up’ to the status of canon. However, those who accept as canonical reference books like the Technical Guide call these names canonical.
Fundamentally, it is a choice as to which game you are playing with the artworks, or, to put it another way, which elements you take as comprising the canon. I am quite a bit stricter than most fans: for me, only the shows themselves qualify, but there is no priority to this particular interpretative choice. You should draw your lines where you wish. However, if you can read this explanation without your head melting, you might like to try the short serial here at my philosophy blog, . It digs deeply into the ways that authenticity, canonicity, and faithfulness apply to collections of artworks ('megatexts') like a sci-fi series.