[chhs]

V2 definitely makes it easier, but it's possible to identify files with V1 by iterating through metadata looking for files with the same length as a local file, then checking each piece against the local file. If they all match, then it's the same file. For boundary pieces where it consists of multiple files, I think it's safe enough to ignore if all of the remaining pieces match the local file, but you could do a more complex search looking for sets of files that all have the same length, and then compare the piece hash with the local files.