excuse the copy and paste, but the following on bevel angles and asymmetry should answer everything here:
In general, there is not going to be an exact angle that is correct, but rather a range of angles that works. For instance, most double bevel Japanese knives will work well with angles somewhere between 10-15 degrees per side. The closer you are to the 10 degree side of things, the sharper the knife will feel, but it will also be more fragile, brittle, and may not hold its edge as long. The closer you are to the 15 degree side of things, the more tough and durable the knife will be, though it wont feel quite as sharp. Its also ok to go even lower or higher than this, depending on your personal preference, though I often recommend staying within this range until you have a better understanding of how things work for you. For what its worth, Japanese craftsmen aren't measuring the angles when they make or sharpen the knives either. Lastly, it's important to keep in mind that you don't have to always use the exact same angle. If you want your knife to feel a bit sharper, go a bit lower. If you need a more tough and durable edge, go a bit higher. So, like I said before, take this info and then decide if you want to spend more time sharpening on one side or the other, and at what angle you want to sharpen in order to get the knife to cut the way you want it to.
Asymmetry, it seems, is also a rather confusing issue for many. Part of the confusion stems from the fact that many of the ways that we describe these asymmetries are gross oversimplifications. For example, the ratios like 50/50 or 60/40 don't really describe anything of substance. Is it the ratio of the percentage of sharpening on each side? Is it a ratio of the angles on each side? In reality, it's neither. No craftsman in Japan it's there and measures angles or ratios. What really matters is the way that the knife cuts. The asymmetry deals with two main issues-thinness behind the edge and steering. The more asymmetrical a knife is, assuming the angles are equal, the thinner the knife is behind the edge. However, the more asymmetrical the knife is, the more likely it is to steer. It's also important to keep in mind that the angles are not always equal. When figuring out asymmetry for any given knife, the first thing that you want to do is cut with the knife. When you cut with a knife, you want to assess whether it is steering to the right or to the left, and how easily it moves through the food. If you notice that your knife is steering to one direction or the other, you want to create more surface area on the side that it is steering towards, so that the knife cuts straight. This can be done by adjusting the angle (either more or less acute) and/or adjusting the amount of time spent sharpening on each side. If you notice that the knife is wedging in food as it goes through, this may mean that you need to sharpen at a more acute angle, or that you need to thin behind the edge. Some of this can also be dealt with through adjusting asymmetry, as previously mentioned. Does that make sense?
Anyways, the point here is to worry less about what the manufacturer did and more about what you want from the knife relative to your intended use and experience. And, on asymmetry, instead of arbitrarily imposing something without any real reason or logic, use the knife, see how it works, and come up with a plan for sharpening from there.
