step,rule,n_before,n_after,n_removed,rationale
1,restrict to regression window 1960Q1-2019Q4 (1959Q4 levels used only for differences),319,240,79,unit: quarters (union of both series 1947Q1-2026Q3); window fixed by TASK.md; quarters 1947Q1-1959Q4 and 2020Q1-2026Q3 out of window
2,drop window quarters with missing du or g,240,240,0,none expected