Unfortunately there is not a real good way to tell other than adhering to a naming convention. I use the following: firewallname-yyyy-mm-dd-hh-mm (year, month, date, hours, minutes). This way I know what is what.
What can occur is someone makes a change to the file but doesn't upload it. Thus the date stamp in the file system shows one date, but that doesn't make it the most current file. This can still happen with the naming convention I use, but it is at least a little more intuitive than trusting date stamps.
By default, when you open the configuration policy editor, it will prompt you to save the current running config. using the FB IP as the name. It will only do this however, if the current file on the WCC station is older than the one running on the FB. If they are the same, it will not prompt to save. Therefore, if you are not being prompted to save the file, then the one on your WCC station should be valid.
Sorry for the long answer. Hopefully that helps.