I'm using the latest version of bitcoin core, also 12W7RgjugzpULqwfq1tCzdU89LZnvVvJVw was the only key in my address book so just backing that up doesn't save my coins?
Then you should be using 0.13.0. However, you did not backup the wallet, so you did not backup the master private key. Most good wallets will not reuse the same address, and many do not tell you what the change addresses are. You *WILL* have change addresses. It is not good enough to backup the addresses that you know about because you *WILL* be using change addresses that you do not know about. You must backup the entire wallet. Since you have not, your Bitcoin is lost. There is nothing that can be done about that.
what bitcoin wallet do you use?
go to blockchain.info to check your addresses on what transactions took place.
Please stop spamming and read the thread before you post.