Arguments about what officially counts within a long-running franchise recur endlessly without resolution. This is not a failure of the participants; the question does not have a determinable answer.
Material accumulates faster than anyone can reconcile it
A franchise running for decades produces films, series, books, comics and games, made by different teams at different times.
Nobody involved in the later material has read all of the earlier material, and contradictions enter continuously without anyone noticing.
The body of work is therefore inconsistent by construction, and no reading can make it consistent without discarding something. Every proposed resolution is really a proposal about what to throw away.
There is no authority everyone recognises
Rights holders issue declarations about what counts, and those declarations are commercial decisions taken by whoever owns the property at the time.
Ownership changes, and new owners routinely reverse earlier rulings, which demonstrates that the rulings were never descriptions of a fact.
Audiences observe this and reasonably decline to treat any particular declaration as final. A ruling that can be reversed by a sale is a policy rather than a fact about the fiction.
Creators contradict each other and themselves
Statements made in interviews are frequently treated as authoritative, but they are made informally, sometimes about work the speaker did not write.
A creator's later intention does not automatically govern what an earlier work contains, and creators change their minds.
Treating these remarks as rulings imports a further layer of inconsistency into an already inconsistent body of material.
The argument serves a social function
Disputes about canon are a way of demonstrating knowledge and establishing position within a community, which is why they persist independently of any answer.
An argument that could be settled would end, and the participants would lose the thing the argument was providing.
This is why proposed resolutions are usually rejected by both sides rather than adopted by one. A settlement offers nothing to people whose standing depends on the dispute continuing.
The practical position most people adopt
In practice, audiences maintain personal versions, treating some material as central and disregarding the rest without needing anyone's agreement.
Rights holders effectively do the same, building new work on whatever is useful and quietly ignoring the rest.
The disagreement is therefore not about facts but about which selection is legitimate, and that is a question of preference presented in the language of rules.