Podcasts showing up as not downloaded when they are in the folder

Hi there, annoying problem just come up with my iTunes regarding podcasts.

Machine is Windows 7 64 Bit running iTunes 11.3. I have put off upgrading iTunes, but since it's been working fine for over a year on this version I'm not sure it's related to this.

Everything has been (mostly) peachy for years.

However yesterday a very large podcast I have dozens of episodes downloaded from decided it had no episodes downloaded.

This is NOT the bug where it deletes them after playing. I made sure it shows all the feed and keeps them after playing them. Problem is it's done it to all episodes, played and unplayed.

No, what it shows is that every episode but the one downloaded that morning has the 'arrow cloud' icon indicating it needs to be downloaded. The mp3 files all exist in Windows Explorer, but they are no longer associated in iTunes.

Normally I can click and drag the files across and it will relink them. No luck still.

Any ideas? I don't want to resync my iPod to get the new episodes but lose all the old ones I've not listened to. I also don't want to re-download dozens of podcasts.

Any help would be greatly appreciated.