“… 40 years after the internment camps closed—President Ronald Reagan signed the Civil Liberties Act, which offered a formal apology and paid $20,000 to each survivor.”
The key difference here, is that Japanese-Americans were imprisoned, and as such there were records about who, when, where and how long people were imprisoned.
That makes reparations very easy - if you were imprisoned unfairly, you were entitled to payment.
You can easily read "identified as ‘Black/African American’ on public documents", "proof of residency", "Record of attendance", and other things which require evidentiary records.
Even "Descendant of someone enslaved through US chattel slavery before" requires records.
That makes reparations very easy - if you were imprisoned unfairly, you were entitled to payment.