The essential difference between Punch and Casor is Punch was given a life sentence as a slave in a criminal case after running away before the conventional term of indenture had ended and Casor was declared a slave in a civil suit after the conventional term of indenture had been fulfilled. Criminal cases are about exceptions to what is expected — they usually involve punishment. Civil cases are about fulfilling what is expected — they usually involve restoration of some sort.

The 1641 law seems to be about formalizing the buying of slaves, which had been happening since 1619. It doesn’t seem to address keeping anyone as a slave for life or treating them differently than indentured servants were treated — if anything, its reference to people selling themselves says the 1641 law ensured that slaves and indentured servants would be treated the same. That’s why people argue about whether the Punch or the Casor case created the first legal slave (ie, life-long slave who was treated differently than indentured servants) in the colonies.