I'd speculate that, 125 years ago, if a tintype came out like the PSH example from Sundance, the photographer would have tossed it in the bin, and told the customer "sorry, we have to do it again". So in that way all the duds are lost to history, and only the keepers survive.
I'd also speculate that a metaphysically perfect tintype, produced today, would have comparatively little appeal to the celebrity crowd.
The fact that the process is so hit and miss, a fact that is proven by the high(ish) proportion of "duds", is part of its appeal. In 2014, there is just nothing impressive about taking a perfectly focused, perfectly exposed, perfectly white-balanced, razor-sharp photograph. Any fool with a smart phone can do that.
That's why there was a tintype booth at Sundance in the first place. It gives the pretty, plastic, celebrity people a feeling of authenticity. I can see how that would be very meaningful to people who live inside such an artificial bubble.
People who take the craft seriously make a fair point that the work could have been done much better, but they are pursuing an entirely different aesthetic.