Wow, I didn't know there are different strategies based on the wallet. The wallet I'm using in Bitcoin-QT.
From what I am reading above is that it doesn't matter how old the backup is, as long as no new addresses are created after the backup.
But if many transactions are sync'd into the wallet after the back up was created. Would the back-up, when used to restore the wallet, just sync all the transactions from the block chain that happend after the backup was created?
Making backups does nothing to the block chain, correct? So it doesn't matter when the back up was made, it will just fill in the missing transactions based on the block chain.
I just have this stupid idea that when you make a new backup, the old back up will just pick up from where the new one was made. You'll end up losing anything that happened between the two back ups.