# Coverage and gaps

Distinguish the advertised collection schedule from what was actually retained.

## Check the live coverage
Use the [live coverage table](/coverage) and each response's coverage notes. The [endpoint catalog](/data/endpoints.json) describes feeds and access. Earliest retained dates are source-specific; do not infer them from the tier's maximum history window.

## Frequency
A scheduled collection is an attempt, not proof of a successful observation. Compare actual collection timestamps and visible freshness information. A source that did not publish and a collector that failed are different situations.

## Missing intervals
Preserve gaps rather than filling them with zeros or forward-filled claims of new observations. Document which sources and date ranges your query covered. Publication date can differ from the first date the archive saw a document.

## Historical completeness
The archive contains what was retained. A longer paid history allowance cannot recover a publication that was never collected. Use source-specific earliest timestamps and observed intervals when estimating completeness.