You will understand that as outside users no-one on here knows exactly how the iTunes Store works. However, though the Store caches the feed it would seem certain that the cached version representing the last time it was checked and was working in whatever form. What you see in the Store now represents the cached version. Since it goes up to 15th April that would seem to be a good version (the corrupted version was presumably unreadable and so hasn't wiped what shows in the Store).
Whether you can get a copy out of them is something I couldn't possibly say. All you can do is email them at podcasts 'at' apple,com and ask them nicely. You mght be lucky, but I wouldn't get your hopes up too much.