Reachable is not the same as observed
A peer can advertise an address that is offline or inaccessible. Only a successful handshake qualifies as reachable. Observed IPv6 addresses may appear before any are confirmed reachable from the crawler's network. Check age also matters: the latest stored status is not a guarantee of present availability.
Why trackers report different numbers
Discovery sources, retry policies, timeouts, IPv6 and Tor connectivity, freshness windows and geolocation coverage all affect results. Compare definitions and collection times before comparing headline counts. One operator can expose multiple endpoints, while private or outbound-only nodes may not appear at all.
What the timestamp means
Atlas's API field last_crawl_time is the latest observation or check, including manual node checks. It does not certify the completion of a scheduled crawl. Country and version reads can reflect a slightly different moment; frontend aggregate data may be cached for about a minute.
From a snapshot to research
No historical aggregate series is published yet. Read how to interpret changing node counts before inferring growth. For exact count definitions, see Atlas methodology and the node data glossary.
Running a node need not change the public count
You can validate using outbound peers without being publicly reachable. The Build a Bitcoin Node guide explains the setup choices; the node checker tests optional public P2P access.