I created a python script to solve the intermittent lack of original air date in my xmltv feed from zap2it. Some shows have it, some dont. Regardless, if you are using xmltv as your guide data, this may work out for you, or it may not. I created it to solve a specific circumstance where plex wouldnt record TV shows, like local news broadcasts, that didnt have a different original air date on it.
