1step,rule,n_before,n_after,n_removed,rationale21,drop GDPC1 quarters without a complete 3-month UNRATE quarterly average,319,314,5,UNRATE starts 1948-01 (1947 quarters have no unemployment data); 2025Q4 has a missing month32,drop quarters whose first difference cannot be formed (previous quarter missing),314,312,2,first available quarter (1948Q1) and the quarter after the incomplete 2025Q443,restrict to regression window 1960Q1-2019Q4,312,240,72,TASK.md information rule: quarters outside 1960Q1-2019Q4 must not enter any estimate5