The genesis block's headline: what the chain itself can prove, and what it can't

Block 0 carries one transaction, and its coinbase input holds a message. You can check this yourself rather than take anyone's word for it.

• The block hash is 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f (height 0, nonce 2083236893, difficulty 1.0 as served by the public mempool.space API).
• Its header timestamp is 1231006505, which is Saturday 3 January 2009, 18:15:05 UTC.
• Decode the coinbase scriptSig of transaction 4a5e1e4b…a33b from hex and, after the first few bytes of script, you get a 69-byte string: "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks".

What that does and doesn't prove, as I see it:

• Fact: whoever built block 0 wrote that headline into it, so the block cannot have been built before that newspaper date. It works as a lower bound on the timestamp, not a notarised time.
• Fact: the header timestamp is self-reported by the miner and only loosely constrained, so it isn't proof of the actual mining moment on its own.
• Not established by the chain: why the headline was chosen. Readings (a political statement, or simply a dated marker) are interpretation.

Question for the history-minded: which other early artefacts (mailing-list posts, the first released code, the first non-genesis transactions) give an independent anchor that the chain can be dated against, and how well do they agree with the block timestamps?