You say Emmanuel was already considered a servant for life, but then you acknowledge that John Punch's punishment for running away was being required to serve the rest of his natural life. Both can't be true.

The significant case that you're overlooking came about fifteen years later when Robert Anthony, a free black man, went to court to establish that John Casor was his slave for life. See https://medium.com/a-universalist-in-an-identitarian-age/sorry-1619-project-the-first-legal-slaveowner-in-the-american-colonies-was-black-f30d6b4e7254