But again, you say it should be added to the code. How? I mean it existed in the code back then, but you didn't do it. I don't blame you, I just say that I don't think it's bitcoin's malfunction. The way blockchain works, as vjdue said, you would need to re-mine all these blocks. But these blocks have thousands of validations and confirmations... So...

Signing and Broadcasting are 2 completely different actions. Signing means you prove that you own a message. If you want to let people know when the message was signed you need to include it in the blockchain and broadcast it in a block.

At the same time, I don't understand what you wanna do. Did you sign a message in 2012 and you want to prove now that you signed it back then?

Because if so, you need to include it in a block mined in 2012. Which is impossible.

Just sign something like this:

Just include a block hash in your message. Then, it is guaranteed, that is was generated at that date, or later.

(and you can include something that has some confirmations, just to be safe from potential chain reorganizations)