I’m not sure if I get the relevance of your point. In the state of nature that Blackstone describes, I arguably would have the natural right to submit to a condition of slavery, binding myself to another person’s command and thereby give up my prior natural right to self-ownership or liberty in exchange for some consideration such as a payment or even just not being killed by a conqueror. In civil society slavery (the absence of self-ownership or individual liberty) was universally recognized to apply to some individuals throughout recorded history until the Nineteenth Century. Hence liberty was alienable both in the nature and in civil society until slavery was abolished by law.
When Jefferson described liberty an an unalienable right he was expressing an aspiration for the future, not a then current fact.
Yes, you miss the relevance.