Quote from: jnano on October 29, 2017, 11:28:27 PM

I thought maybe there are repeated tx ids, or auxiliary data that clients can theoretically add in.

You can't have two transactions with the same tx id in the blockchain, as tx id is calculated based on transaction contents. If that was possible you would be able to send the same transaction twice, meaning you would spend the same coins twice and double the balance of the receiving address.

Quote from: aplistir on October 30, 2017, 10:28:12 AM

In my opinion it is nuts to keep that much BTC in one address. What if someone accidentally got an address collision with them?

P2PK is actually safer from address collisions that P2PKH. To be able to spend from P2PK input you have to use exactly your private key. There is only one of those. Paying from P2PKH input there are 2^96=79228162514264337593543950336 private keys that can be used. Finding one of them accidentally is that much more probable.

To be honest, address collisions are so unlikely that you are more likely to invent a quantum computer in your garage big enough to break those public keys and far more likely to lose one of the private keys if you keep your coins in multiple addresses. Pretty much anything in this world is possible thanks to quantum mechanics, but you have to be reasonable and not spend your time calculating practical impossibilities.