Hi Inversion,
Great question! We’d love to know what the answer is. 
Admittedly, our area of expertise is not blood donations. As noted in the competition, this is where the data come from:
https://archive.ics.uci.edu/ml/datasets/Blood+Transfusion+Service+Center
As far as I can tell, the original paper that uses that data isn’t available outside of a paywall, so it may be a challenge to get more detail (though, I know some people have luck with #icanhazpdf on twitter.)
Sorry that’s not very satisfying, but we’d definitely be curious to hear any results you turn up. Thanks for bringing it up!
Peter