Offering rewards in advance is not the same psychologically as receiving surprise rewards because of work already done. Also while I'm familiar with the debate

Offering rewards in advance is not the same psychologically as receiving surprise rewards because of work already done. Also while I'm familiar with the debate around incentives for blood donations that particular paper you have cited is terrible. Notably they do a literature review where they find discussions about how it could theoretically undermine motivations, but don't address the counter-argument they mention themselves where they list example of rewards being used to successfully increase supply! They list studies where it both decreased and increased supply, which seems to indicate that the type of incentive and the conditions in which it was offered make a significant difference. They end up arguing that there are risks that incentivized donors come from groups of higher risk of infectious blood diseases. This may or may not true, but is a different argument to if incentives work.