I found very interesting info on those bayo: apparently, the ones that are coming from mother Russia, are not 100% original. IF you see the blade been darkened, it means that the hardness of the original blade has been reduced to not to exceed 25 something....( I guess some kind of measurement unit). The reason been is that it is considered a "cold weapon" by Russian law and is illegal to posses without a special permit. This reduced hardness makes the steel much softer and according to what I've read the blade become almost flexible....
Again, that is the info that I found on Russian site so please do not shoot the messenger...