When you did (3), it would be showing the balance for the account that showed up for (2)--the unregistered one--does it show the balance you are missing/expect to belong to your account?
Yes when I do (3) it shows exactly the expected balance.
Do not worry, this means your funds are safe and accessible. We just need to figure out the proper way to fix your wallet depending on whether your account was registered or not.
As a temporary solution, you can try doing "wallet_account_rename <old_account_name> <new_account_name>", replacing <old_account_name> with your account name, and replacing <new_account_name> with some other name. If you do this, does the account with your balance now show up for you under the new name?
Did you register your account name? If not, it's possible that someone else registered that name and that is what is causing the display issues in your wallet.
I am not 100% sure, but yes I think I have registered it. And the date of registration displayed when I do (1) fits with the hypothesis that I have registered it (the displayed registration date is the same as the date on which I logged to my wallet and sent some BTSX, and as I didn't log to my wallet very often besides that, the likelihood is high that this was me who did the registration that day).
Unless you totally don't care about recovering that account name, we can also try to recover your account if you did indeed register it:
4. If you run "wallet_dump_private_key <account_public_key>", replacing <account_public_key> with the keys listed for the two duplicate accounts from (1), do you get anything for the registered one?
5: If you run "wallet_account_transaction_history", do you have any transactions that show up as registering that account name?