Placement observations
Unknown includes timeouts, rate limits, robots exclusions, challenges, login walls and pages a plain fetch cannot read. An unknown result is never a removal finding.
Observation and confirmed loss are different
One complete absent observation describes one check. Confirmed placement loss requires two complete absent observations at least thirty minutes apart. Unknown attempts preserve the last known observation and carry uncertainty; they cannot supply the evidence needed for loss confirmation. The local ledger keeps intent and observations separately. Its default CLI exit behavior also preserves unknowns: a successful exit alone does not prove every expected link was found.Destination health is independent
Destination checks inspect the exact target URL. Results usehealthy, unavailable and unknown, with HTTP status, redirect and timing context where available. A 404 or 410 observation can report unavailable; confirmed unavailable state requires repeated evidence under the thirty-minute rule.
A source page can still link to a destination that is unavailable. A healthy destination does not prove that a source page links to it. Consult both placement tools and destination tools when investigating a broken citation.