Canon is defined as "a list of the works of an author that are accepted as authentic". In terms of shared universes with multiple authors, not to mention other sources of data or speculation, sometimes there are differences of opinion.
Some people like to know exacty what's true and what isn't, so that they can engage in reasoned debate and sharing of opinion on the fora. So we've got to working on what is 'truer' than what.
The current , vaguely official, priority.
- Official Canon: In a published product. These break down into
- Discussion: Comments made by official people in a public arena.
- Apocrypha: Deductions by anyone else based on harder information.
- Speculation: Guesses.
- Creative Commons: Stuff we make up.
A list of Sky Battleship names and classes in a published product would be Official.
A comment from Randall Bills confirming that the list of classes is exhaustive would be Discussion.
If we can use those two pieces of data to work out that a particular named Leviathan belongs to a particular class, that would be Apocrypha.
If we were to look at the list of Sky Battleship names and notice that they matched the existing Battleships in real world history at that time, except for one that was missing, it would be Speculation to say that there's a Sky Battleship in Leviathans of that name.