something else to keep in mind is that it is sometimes hard to vote in the united states if you're black, and, contrary to public perception, those concerns continue to be real in the democratic primary, as well.
in past years, i would have suggested that this would benefit biden at the expense of sanders, as they'd have done the research. this year, i'm not convinced that this is where the establishment has it's thumbs. it's a good experiment, actually. if biden ends up with 60% of the vote, you'll know why; conversely, if sanders pulls out a surprise upset, you may want to start asking some questions about voter suppression.
but, if there are accessibility issues, it will certainly help the candidates that do better with white voters, regardless of which class of black voters gets targeted.