The approach I suggested in my last post will complete the file for you even in this case, if it can be completed with what you have. (Only exception is when a part is incomplete in the import file, and there's some corrupted data in the part file, but that goes far from the straight path...)
If part 2 can be verified in the import file it will be taken over, and the downloaded part 2 will be dumped.
GonoszTopis intention was: if you try to import something that doesn't fit at all the process should not make any more gaps. That's fulfilled.