1step,rule,n_before,n_after,n_removed,rationale21,keep (origin,horizon,model) forecast pairs whose target month exists in first_release.csv,80,80,0,all 20 target months (10 origins x 2 horizons) have a first-release actual32,keep pairs with a non-missing forecast,80,80,0,all vintages have complete history from 1992-01; no missing levels4