I like the comparison to manga and the deeper questions of canon nature you bring up here. Ultimately this point of view assigns more responsibility to the artist of each version or fanfic. They have the responsibility to do world building over again so that the plot can support suspension of disbelief the characters need to become real for us.

In the Chosen commentary, Joss stated that he told Sarah Michelle Gellar that Buffy meant it when she says "I love you," and he told James Marsters that Spike believed Buffy loved him even though he was saying that he didn't.,

I have to wonder, though, if you have a different DVD commentary from the rest of us. That's not what Joss said on my Chosen DVD.