step,rule,n_before,n_after,n_removed,rationale
1,merge vintages (latest vintage per month) and restrict to window 2001-01..2026-09,957,309,648,months 1947-01..2000-12 outside the summary window (still used as 12-month lags)
2,drop months with no index level P_t in the latest covering vintage,309,308,1,no interpolation/imputation allowed
3,drop months with no index level P_{t-12},308,308,0,no interpolation/imputation allowed