From the conclusion
We also note a strong post-award citation gap that shows no sign of diminishing over time. On average, at five years after the award conferral, Clark medalists have 1.92 more weighted publications than the synthetic control group. Furthermore, Clark medalists attract 18.35 citations per publication, whereas the control group attracts 12.27, demonstrating a difference of 6.08 citations per pre-award publication. After another five years, the difference in weighted publications has grown to 2.46, whereas the gap in citations per article amounts to 14.02. Ten years after the award conferral, Clark medalists and the synthetic control group respectively attract 32.12 and 18.1 citations per publication on all articles published before the award.
Probably winners of the JBC Medal keep producing (as oppose to other winners, such as winners of the math field-medal) because the JBC Medal is a good indicator/inspiration to get the Nobel Prize in Economics.