I wouldn't call them 'missing lyrics'. They might be called alternate lyrics. Over the many years that this song has been popular and spread beyond the Spanish-speaking realm, the story has changed and ramified. There is no version that has 'all' of the verses, because they would contradict each other. The music also differs from version to version.
'Del Gato' is simply a mis-hearing, or mistake in transcription. Natalie Merchant made the mistake in one or more of her concerts.