Is every 00-liner 5th gen?

No. Birth year and debut generation are different axes.

Why do two charts disagree?

Year-only sources, timezone, or mixing Korean vs international age.

Ages · 아이돌 출생연도 코호트 — ‘00라인’·세대 이야기를 신중히

アイドルの出生年コホート

Cohort = birth year cluster (e.g., born in 2000).
Generation = debut-era marketing buckets (see our generations cheat sheet).
Verify with full birth dates on the ages hub; year-only lists can mis-rank people born in December vs January.
Etiquette: cohort memes are fine; using them to dunk on “too old / too young” is not useful facts.