Mary's post is very interesting. Folk process at work. None the less, many shanties about Santa Anna clearly refer to incidents in the life of the Mexican general. I suspect therefore that the sailors having had old songs passed down without full understanding of them, adapted the tunes and some of the words - or what they understood the words to be - to events of their own times. Most of the references reverse actual history vis a vis the victors in the conflicts between Mexico and Texas and the USA. Being British shanties, and the British sentiment in the mid 19th century being still firmly against the rebellious former colonies, this is understandable.