The September 6, 2008 RockFest schedule lists Bear the Astronot twice. It’s one festival date, with an afternoon set at Club Red and an evening set on the Red Owl stage. An import that deduplicates on performer and date would lose half the record. An import that treats every row as a separate event would hide the connection between the two sets.
What should the archive store?
Give the event its own record. Give each set a time, stage, and credited performer. Attach the promoter’s original schedule so someone can check how those fields were interpreted. If a flyer gives you a date but leaves the year off, preserve the printed date and record where any later year came from.
That small example is close to what we run into in Mission HQ. The same work can show up in a release feed, a press page, and an archive. You need a reliable record underneath, plus enough provenance to resolve a discrepancy six months later. That matters just as much for a 2008 booking email as it does for a new release.