Classic challenges are filtered by when a title aired: a decade, a range of years, or a century-spanning list. Most are worth 3 points.
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Because eligibility depends on air dates, a single requirement can often be filled by many titles. The constraint is usually finding ones you actually want to watch from that era.
Tip. Sort candidates by community score within the era. Older titles have less consistent metadata on AniList, so double-check start dates.