It's not so much the distance of the lava over the ground. If you carefully pop the cork from a champagne bottle, it does not overflow. Be somewhat less gentle, and the stuff overflows from the top and drips down the side, maybe you get a bit of rise. There are volcanos that look like this when erupting. Shake vigorously, and the cork will launch itself on a fountain of bubbles. That's a volcano lik Mt. St. Helens. For a supervolcano, the champagne bottle is insufficient as a simile. Think broken fire hydrant. The problem is the enormous amount of lava going up in the air in droplets and turning into ash, which then gets spread around the atmosphere around the world.

I have no "farthest ever", but did find this artice on Wikipedia for you, including a reference to a book on the subject, that states that when Yellowstone last erupted, 6400.000 years ago, the magma and ashes got as far as norht Mexico and covered the USA west of Mississippi.

Hope that helps.

Here is an article from the FOSS Patents Blog with some details on the case ruled on in last August in the Netherlands, which is what I guess is being referred to as "earlier dismissed in Europe". It's certainly amazing how one judge can say "this clearly existed before" and another can say "no it didn't" based on the same info.