Good points, thank you!
Yes, it's probably better to check that len(components) is exactly 4, as more than 4 would also be a problem. (I initially posted the fixed code checking against 3, then noticed my error and edited my above post.)
In fact I could probably be doing a lot more validation here, like adding a whitelist for known awards or to make sure that the rank field looks right (i.e., is a known word or a positive integer). Since this template is for transforming metadata on the fly while loading books onto my device, I will probably repurpose that added validation elsewhere as well, e.g. to show me a warning icon in my library view for books which fail.
Thanks again for the debugging help! <3