step,rule,n_before,n_after,n_removed,rationale
1_unverifiable,drop months < 1999-01 as targets,345,333,12,1998 yoy values not verifiable from levels in file (README says they should be empty)
2_availability,keep target months <= origin-2 (2026-02-01) at last origin,333,326,7,GDP publication lag: target must be observed at the origin
3_lags,"drop targets whose regressors y_{m-3}, e_{m-2} precede 1999-01 (h=1)",326,323,3,regressors must be verifiable observations
4_covid,drop pairs with target or regressor month in 2020-03..2021-12 (h=1),323,298,25,"pandemic outliers and base effects; pre-specified, known at first origin"