1step,rule,n_before,n_after,n_removed,rationale21,window 2001-01..2026-09 drop months with no index level P_t in the sources,309,308,1,no imputation of missing levels (empty cell in 2026-10-28 vintage)32,drop months whose lagged level P_{t-12} is missing,308,308,0,g_t not computable without P_{t-12}; no imputation4