When skeet shooting started, it was common to build a gun with two different chokes. Today, both barrels of a modern skeet gun are choked the same. Of course, shell quality has improved greatly since the early part of the last century when skeet was born and that has a lot to do with it. So also does the fact that skeet today permits a pre-mounted gun which makes it much easier then the original game which required low gun. Skeet 1 is roughly equivalent to today's standard skeet choke.
Different countries have very different choke conventions and names.
I've often considered Skeet 1 and Skeet 2 to be just about the ideal 12 gauge upland bird chokes. They should give you about equivalent patterns at 20 and 30 yards. These are very realistic hunting distances in the real world for shooting over pointing dogs or woodland hunting. Not bad for timberland or decoyed ducks either. Out West with skittish mountain chukars, you might want more.