Every day at 00:15 (Madrid time) we record every pick published the day before in a fingerprint: a hash tree whose root is sealed in Bitcoin with OpenTimestamps. Anyone can check that a pick existed that day with that content, and whether it was changed or deleted later.
Not in any fingerprint
It was published before the daily fingerprint existed, or it is a pick imported from a history.
How to check without trusting us: the leaf is SHA-256(0x00 + content) and each step SHA-256(0x01 + left + right). If the path reaches the root and the .ots verifies with the official OpenTimestamps client (ots verify), the pick was recorded that day. This proves when it was published and that it wasn't touched; it says nothing about whether the pick is good.