if there is a torrent of the original file...
That sounds like a good idea.
You could also split all 3 files into small pieces (make copies first of course), maybe 2000 1mb pieces*
. Then compare set A against set B using something like beyond compare. Copy one set of files that were tested to be exactly the same to folder D. Then compare A to C, copy another set of duplicates to folder E. Then compare B to C, copy one last set to F. Compare D to E, all the files that are in both D and E should be exactly the same with a few "orphan" files here and there. Sync the 2 folders so you have all the same files in both D and E, then delete one of them, say E. Then compare D to F, sync them, and delete one, say F.
Folder D should have one complete set of all the files, the best bet for accuracy since every file in it got downloaded at least 2 times exactly the same way.
Unsplit the files and check the MD5 again, hopefully it'll be correct.
If folder D is missing any files, I guess you're stuck with doing compn
's idea (which might be easiest if you already have uTorrent or something and there is a torrent available) or I guess you could stick the missing files in from folders A, B, and C in a systematic manner (might get pretty complicated if there's more than like, 3 missing files).*
Although I haven't actually used this feature, I think Directory Opus will split files, if you don't have it there are tons of file splitter programs out there. I don't remember the reasons why now, but of the programs I've tried "The File Splitter
" is the only one I've kept.