Ben,
I believe the Zenith set was previously discounted as being first if you read Tom's website, History of Television the First 75 Years and the above quoted thread. The owner of that Zenith himself said it was a prototype.
Edit: This is the thread with the Zenith discussion.
http://www.videokarma.org/showthread.php?t=22010
2nd edit: Further documentation here:
http://www.visions4.net/journal/chromatron/