Should outside evidence from an interview have any value on the interpretation of a work?

I asked a question here on StackExchange about whether Meredith Vickers is an android or human in Prometheus, the new movie. Most of the answers cited evidence from the movie supporting their answer one way or another.

In Prometheus, is Meredith Vickers a human or android?

One person cited evidence from an interview with Ridley Scott. In the interview, RS reportedly states that Vickers is definitely human. I informed the person that evidence outside of the work (the move) is completely irrelevant. He disagreed.

Isn't it almost universally understood and agreed upon that a creator's interpretation of a novel, movie, song, or other work, is just another interpretation? What Ridley Scott says about Vickers' humanness might give me insight, but it's not evidence.

My question is whether evidence such as interviews, interpretations, or opinions, provided by creators or actors regarding any work should have any value on the interpretation of the source?