## TL;DR
A missing index.json in an EDGAR filing directory usually means the filing predates the JSON index or the directory listing is served as HTML only. Parse the directory's HTML listing for exhibit links, or construct exhibit URLs from the filing's accession number and document names.

## The error
```text
GET https://www.sec.gov/Archives/edgar/data/1234567/000123456726000001/index.json returned 404
Filing directory exists; exhibits (EX-99.1) unreachable via index.
```

## Fix it
1. Fetch the filing directory URL without index.json and parse the HTML table for document links; the exhibits are listed there with their filenames.
   Expected: Expected: the HTML listing shows EX-99.1 and other exhibits with direct links.
2. If you know the exhibit filename pattern, construct the URL directly: Archives/edgar/data/CIK/accession/EX-99.1.htm and verify it returns 200.
   Expected: Expected: the constructed exhibit URL loads, bypassing the index entirely.
3. For older filings, check for a .txt complete-submission file in the directory, which bundles the filing and exhibits in one document.
   Expected: Expected: the full-text file contains the exhibit content inline.
4. In the pipeline, prefer the HTML directory listing as the primary exhibit discovery method and treat index.json as optional.
   Expected: Expected: exhibit extraction works for filings of any vintage.

## When to use
- Your exhibit extraction fails because the filing directory has no index.json.
- You need EX-99.1 press releases from older filings.
- You run exhibit ingestion across filings from many years.

## When not to use
- The whole filing directory 404s - then the accession number is wrong.
- index.json exists but lists no exhibits - the filing genuinely has none.
- You only need the main filing document - skip exhibit discovery entirely.

## Why it happens
The JSON filing index is a newer EDGAR feature. Older filings, and some filings processed through alternate pipelines, only have the classic HTML directory listing. The exhibits are all there; only the JSON convenience layer is missing.

## Variant phrasings
### edgar filing index.json 404
Same failure and fix; some searchers phrase the query this way.
### sec filing directory no index.json exhibits
Same failure and fix; some searchers phrase the query this way.

## Edge cases
- Some directories list index.json but it is stale relative to the HTML listing; trust the HTML.
- Exhibit filenames are not fully standardized; always discover from the listing rather than guessing.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_3PRbSyZ0r12umHvXo_l5RQ