‘Canonicity’: the Book or the Reader?

[Lalwendë]

Originally Posted by Bethberry

Readers might well indeed decide that in this case his work does support or demonstrate this distinction between allegory and applicability, but readers are not bound to automatically accepting his definition.

I'd agree with that, as readers will inevitably come to a variety of conclusions (some may choose to ignore what Tolkien said, while others may have simply omitted the foreword in the rush to read the story). So while we are not bound to accept Tolkien's definition, I have to ask, ought we to accept his definition? Does LotR make more sense if we do?