Every contact that Full Pipeline's Target Contact / Exclude Rules classifier rejected gets archived here (prospect_contacts_deleted) — never just discarded. Browse and search what got dropped and why, export a report, or restore any of them back into a hypothesis group's contact pool so Generate Messages picks them up. This does not cover contacts that were scanned but never reached the rules classifier at all (e.g. a company-name mismatch skipped the whole org) — those are still sitting untagged in prospect_contacts; use Rescue Untagged Scan Contacts for that pool instead.
BDR / group filters query the archive directly; date range and search apply to what's loaded. Loading "All time" with no BDR/group filter can pull a lot of rows — narrow with a filter first if this collection has grown large.