1step,rule,n_before,n_after,n_removed,rationale21,Months 2001-01..2026-09 in the analysis window (one row per calendar month),309,309,0,"Starting frame: every month of the stated window, levels from most recent vintage covering the month."32,Drop months whose own index level P_t is missing in the source,309,308,1,No imputation allowed; missing: 2025-1043,Drop months whose lagged level P_{t-12} is missing,308,308,0,No imputation allowed; missing: none5