Anything starting with a $ inside of ServiceCenter is a variable and is not a field.
You'll find that a number of times when you're looking at data on screen inside of ServiceCenter, you're not looking at the raw data, but rather at a computed value based on that data. For example, when you look at the problem details form inside of ServiceCenter 3.0, you're really looking at a combination of the original problem description (saved in one field), and any past updates (saved in another).
In order to display a computed value to you, the programmer will first compute the value, either in the RAD code, or in the Display format control, and then put the value in question on a form by setting a field's input name to the variable name.
Computed values aren't stored into the ServiceCenter data store, so if you want to export them out by going after the ServiceCenter table structure, you're in a bit of a bind.
Ultimately, of course, the computed value is based on other values which at some point have to be read out of the data store. If you know what the computed value is based upon, then you can just query out the raw data and then do the same computation yourself inside of your application.
So, my question to you is this:
What piece of information are you actually trying to export? I can probably point you at the right field name if you can tell me what you're exporting.
Good Luck.