Half a dozen original compositions I would consider a "slight" exaggeration. A lot of research has been done into this theory, and it is possible that Mozart did commission some works from others and put his name at the bottom. It wasn't such a farfetched practise at the time. In fact, there's talk that he wrote music for others. I can't remember exact names now, but one in particular who wrote some things for him was the organist composer in Venice at the time. All of this hubbub and scandal really brings you nowhere, however. There will always be speculation, doubts, etc. about certain music. I, for one, feel the same spirit in most of his output.