Having crafted a dataset and trying to submit it for evaluation against the "Classifying vocals" challenge, I get "Cannot add this dataset because of a validation error: Can't find low-level data for recording: 1510ce66-eb81-4ad0-abfa-2231947352bb". Instead of erroring out, it should just ignore those Recordings in its evaluation.

1) I know that more than one of the MBIDs I've added are not in AB (some due to bugs in Essentia, like https://github.com/MTG/essentia/issues/192 ) and going through them one-by-one with this error as a guide is going to be a drag.
2) You might want to add a Recording you know falls into a given category, but you haven't been able to analyse it yet. (E.g., if you're at home and the CD is at the office.)