Forecasts come from D6, matched to the Cambridge entries by candidate number.
Forecasts captured in D6 per subject group.
Only subjects the principal has accepted go into the upload. Private candidates are X.
First import: pick the D6 "Cambridge Curriculum Marks and Statistics" export (.xlsx) and the Cambridge forecast-grade entry files (fg_<code>_<centre>_<session>.csv, as many as you like).
Later updates: pick only the new D6 export. That fills in forecasts teachers have entered since, and nothing else: every grade already imported, every review and every accepted subject stays exactly as it is. Nothing is saved until you press Import.