Well yes, all my work is still in TWC.
In the normal export, the values for %0, %1 etc. change depending on which export option you selected. If you created your own export option, then it would be up to you to select the elements for export yourself.
I would suggest sticking to the methods which work as export and then process the resulting file into your XML. Exporting as .csv includes all the hidden custom fields on the tiddlers. It may not be elegant, but it'll get you a data format which you can then use outside of TW.