[im4w1l]

1. Because the hash is in the blockchain, certificates cannot be created retroactively.

2. The notary could make their archive public, so that any interested party could go through and verify that it is legit.

3. By using many different notaries the chance of any one of them being bad would be reduced.

[cm3]

Sure, and if the quorum consists of 6 members, and you managed to undermind 3 of them by making sure they're fed the same custom shadow content, you'll have a split.

[iopq]

You could literally put it in the Bitcoin blockchain. This will be spread among thousands of machines with cryptographic proof.