I don't understand what happened there? If he sent 1 BTC to himself, then the other 8999 should be sent to a change address for which he controls the private key. That is how the deterministic wallets work today. It is not necessary to re-backup a wallet after every transaction, right?
If that is not what happened, how did the wallets back then work? Would they generate a new change address at the time of sending? In which case there was no record of the private key?
This happened before deterministic wallets, which are relatively new.
At the time, the wallet would create a new, random "change" address when the transaction was created. This new address would exist only in the wallet, which would then need to be backed up.
At the time, a wallet was a collection of random addresses that would have to be backed up every time a new address was created. Now, HD wallets are pseudo-random addresses that can be recreated with one master key that doesn't change.
This means if you use an HD wallet, you can eliminate the risky effect of the change address generation, because your change addresses are already generated and stored in the HD wallet itself? So if you don't spend the whole amount of the unspent output, the change will remain in your own wallet, just on the next address, and you won't need to remember the private keys, because your seed will regenerate your HD wallet anytime you need and you will have the control all of the addresses.
Does this also mean that if you use a paper wallet, you need to import the private key into an HD wallet, not to lose bitcoins because of random generated change addresses?