in reply to The Unexplored Territory
The set of dual-lived modules covered by App::DualLivedDiff is not complete but covers only those for which I wrote a mapping. Since I wrote App::DualLivedDiff, Dave Mitchell added the script Porting/core-cpan-diff to the perl core (in 5.10.1 and 5.11.x). It's a rewrite of App::DualLivedDiff that uses the information available from Porting/Maintainers.pl (in core) instead of another set of module/file associations. Maybe you should have a look at the distribution info in Porting/Maintainers.pl (also check out Porting/Maintainers). It's essentially guaranteed to be kept up to date.