Since my, err, experiments with file scanning and an unlucky typo left me with a mostly empty device, I'm running a full re-import, and the import process is logging some warnings for "no spine entry found for TOC entry <blah>" issues
.
Don't know if that's new, though, because the syslog has always been a great place to check if nickel itself hadn't already complained about something funky about a book during the import
.