A brief initial analysis for 2020-01 Quantum Country efficacy experiment. In the control group, most readers got a perfect score; almost none forgot more than two answers. But in the experimental group, most readers forgot three or more answers (out of nine), and about a third of them forgot five or more.
But this seems to be primarily measuring a practice effect, rather than a forgetting effect—and in fact, most of these readers forgot at least a third of the material after just five days without review! See Accuracy rates for withheld Quantum Country questions were roughly equal at 5 days and 1 month (2020 efficacy experiment)
Base accuracy rates vary a great deal across questions: Withheld Quantum Country questions have highly variable accuracy rates (2020 efficacy study).