Explain why each Greatest manga earned its place

docs/greatest.md

@@ -3,6 +3,10 @@
 `greatest.html` is a second, single-page dashboard. The Japanese title is **史上最高の漫画**, romanized **Shijō Saikō no Manga** (“greatest manga of all time”). It displays the [research reading map](manga-reading-map-2026-10-09.md) as ranked five-year cohorts from before 1970 through 2025–2026. Each period keeps its own separator and tile grid.
 Each tile shows a four-line **Why it matters** preview from the editorial rationale; opening the tile shows the complete text under the same heading. The note is a reason for inclusion, not a plot synopsis or a machine-generated rating.
 
+The inclusion rationale should answer **why this title belongs in this particular survey**: a documented award or record, a demonstrable genre/cultural legacy, exceptional artistic craft, or a clearly labelled editorial fit for this library. A synopsis alone is not sufficient. Do not turn the curator's cohort rank into a claim about an external top-10 poll. The 2025–2026 cohort is deliberately labelled as *future-watch* or *provisional*; a recent reader vote is evidence of early enthusiasm, not proof of all-time importance. Specific “first” and record claims need a primary source before publication.
+
+Primary-source checks for selected concrete claims in the seed include [Tezuka's Princess Knight archive](https://tezukaosamu.net/en/manga/559.html), [Guinness on Golgo 13's volume record](https://www.guinnessworldrecords.com/world-records/405899-most-volumes-published-for-a-single-manga-series), [Kodansha's manga-prize history](https://www.kodansha.co.jp/awards/comics/histories), [the 2025 Harvey Award winners](https://www.harveyawards.com/en-us/about/news/harvey-awards-reveal-2025-winners.html), and the official [2026 Next Manga Awards print](https://tsugimanga.jp/winners_announcement/comics) and [web](https://tsugimanga.jp/winners_announcement/web) results. Keep award year/category precise when editing the notes. Statements of artistic merit or personal-library fit are editorial judgments, not measurements.
+
 ## Separation and data ownership
 
 - `greatest/catalog.json` is a versioned, read-only editorial seed in the application image. Entries have stable IDs, debut year, cohort, curator rank, rationale, official source lead, and optional AniList cover/chapter/status metadata. It is **not** part of `library/`, scraper queue, or `data/catalog.json` collections.