That would be very hard to determine tbh since its been so long. Also you forget that legal systems have changed and differ by country. Our (American) legal system is very much Western-based (English case law) but who knows the various legal systems of African kingdoms and villages back then?
DNA is showing where most current people in the diaspora ancestors originated from. So clearly people can see where their ancestors were likely linked to in Africa. Additionally, while many African societies may not have kept written history; they certainly did keep oral history through griots and other sources; so you can certainly narrow down a lot about some of the people who were spirited away. The matters will not be precise, but close enough should do; because millions of people were disenfranchised of their lands, homes and properties.
And we are not using yesterdays laws; we should use today's laws because that the law has become quiet adept at being able to appoint rights to people. Germany was forced to pay England, France and others after the wars; so why shouldn't modern African nations be forced to repay people in the diaspora for the theft of land, materials and family during the trade. They can put the money aside in trust funds to educate every African in the diaspora. They certainly steal enough for the crooked ass chiefs and politicians in their countries; so they need to be forced to pay up.