In February 2019, Jim McLennan wrote about the 20 Diamondbacks relievers. If we assume a half-life of one year, that would predict 10 of them would remain in February 2020, 5 would remain in February 2021, and 2.5 would remain in February 2022. The half-life assumption seems accurate because in February 2022, at most two pitchers (Ginkel and Crichton) will remain.
Another way to look at it, when did the Diamondbacks acquire the 28 pitchers who pitched in relief? Nearly half (13 of 28) were acquired in 2021. That’s what would be expected with a half life of one year.