A third difference is that the Supertags in his converted data do not always fit together, due to the discrepancy between the XTAG grammar and the Treebank annotation and the fact that the XTAG grammar does not cover all the templates in the Treebank (see Section 4.1).
even if the Supertagger is 100% accurate, it is possible that the correct parse for a sentence can not be produced by combining those Supertags in the sentence.