It would be nice if repeating the --fuzzy option made rsync search for fuzzy basis files for a destination file in --*-dest directories as well as the same directory as the destination file.
For reference, this arose from bug 3392; I'm not advocating it myself. (I regret the noise; I think it's important to have a complete record and wish I could achieve that more quietly.)
I have implemented this repeating of --fuzzy to have rsync scan in the alt-dest dirs too.