if there is still payment owed to me should a unconditional waiver for a previous date already paid for?
You should definitely not sign an unconditional waiver in that situation. That all being said, it can sometimes be difficult to determine whether a lien waiver is conditional or unconditional. You may want to have someone review the lien waiver for you. Alternatively, you could simply ask the other side, by email, whether the waiver is conditional or not.
If this is the final lien waiver, it should be conditional. However, your lien rights may have run already if the work has been complete for a certain period of time, so if your lien rights are expired then you don't need to worry about waiving your lien rights (because those rights no longer exist).