Is there an official, citable Universal Category System filename specification (PDF or HTML at a dated version) that I can fetch from the UCS site, or must I rely on tools and vendor pages?

Negative result at the public-web level. At access time the official site (universalcategorysystem.com) publishes no filename-specification PDF or HTML page itself: it links only to resources.universalcategorysystem.com, which redirects into a Dropbox shared folder whose download form is a single 339,633,132-byte 'UCS Release.zip'. The folder listing could not be read without downloading the archive or running JavaScript, so whether a dated filename-spec document exists inside it is unverified. The site's version note is 8.2.1 (January 2024); earlier captures show the repository was Google Drive in 2020 and Dropbox by mid-2023. Curator qualifications: Negative result verified and consistent with the curator's own attempts (C3R-0221: no filename text on the home page, script-rendered resources page). The official material is a large Dropbox release archive (producer: 339,633,132-byte zip), not a citable web page. Rights/verification notes are shown as limitations (L00 0019/ADR-0011): they restrict reuse of the cited material or record what was not verified; they are not cleared by this summary. Limitations: [verification_limitation] Official archive not downloaded (size; disk near the warning threshold; storage policy); whether it contains a dated filename spec remains unverified. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://universalcategorysystem.com/",
      "note": "work/universalcategorysystem_com_ home page; work/dbx.headers"
    },
    {
      "url": "https://resources.universalcategorysystem.com/",
      "note": "work/universalcategorysystem_com_ home page; work/dbx.headers"
    },
    {
      "url": "https://web.archive.org/web/20230626093121id_/https://universalcategorysystem.com/",
      "note": "work/universalcategorysystem_com_ home page; work/dbx.headers"
    },
    {
      "url": "https://sonofex.com/ucs/",
      "note": "work/universalcategorysystem_com_ home page; work/dbx.headers"
    },
    {
      "url": "https://www.jamsoft.co.uk/samplesort/support/universal-category-system/",
      "note": "work/universalcategorysystem_com_ home page; work/dbx.headers"
    }
  ]
}