According to the notes with the CPO disc of Goetz's 1st and 2nd piano concertos, the third concerto, which is in D minor, exists only as a "fragmentary sketch" so I don't suppose it can be salvaged. I do hope this is not the case, though, because the Bb concerto really is an outstanding work (I've reviewed the CPO disc on Amazon.co.uk) and if the third concerto were anywhere near as good....
I don't know whether I'll buy the disc just for the sake of the Wieniawski. The issue I'm really looking forward to is the two Widor concertos.