1step,rule,n_before,n_after,n_removed,rationale21_restrict_window,keep months 2001-01..2026-09 of the spliced monthly level series (1947-01..2026-09),957,309,648,Analysis window defined in TASK.md32_drop_missing_level_t,drop months whose own index level P_t is missing in the source,309,308,1,No imputation allowed (empty cell in 2026-10-28 vintage)43_drop_missing_lag12,drop months whose P_(t-12) is missing in the source,308,308,0,No imputation allowed5