With the advent of modern, high-carbon stainless steels, or alloy steels, forging has become obsolete. These steels were developed for the aerospace and industrial machining industry. Parts made for airplanes and space ships are made to such precise tolerances that it was impossible to forge them. Therefore, super-hard, super-dense steel that could be precision machined had to be developed. Precision machining is what is often referred to as stamped.
I don't know where you got this information, but it is WAY out in left field.
1. Forging is NOT obsolete. It is simply a way of rough forming a piece of steel by hammering it into shape (manually or with an air or hydraulic hammer) to toughen and strenghten it prior to finishing. Blacksmithing is a type of forging. The hammering does what is called "work hardening" to make the blank tougher, more wear resistant, and less brittle.... how much it does so is a factor of how well it's worked and the carbon and other alloy content of the steel. The forging process does not replace heat treating to harden the steel right before finish grinding, just mechanically realigns the crystal structure of the blank. The only time I can think of where forging might not be a better process is in the use of high alloy tool steels, and these generally produce a steel that is too brittle for most normal knives, i.e. it would be too easy to break a thin blade. I've never heard of anything like A2 or S2 tool steel being used for this kind of application.
2. Stamping is NOT machining. It is a method of using a punch press or stamping press to stamp out a rough blank of steel from a sheet prior to finish working it. It generally does so in a single strike. It does not change the crystaline structure of the metal like forging does, it's faster and cheaper than forging, and it produces a lower quality piece of steel.
3. Machining is the process of using various types of machine tools to REMOVE material from a piece of raw stock to obtain a finished product. For a knife, you can start with either a forging or a stamped blank, then heat treat, mill, grind and polish it to achieve a finished blade. I could make 2 knife blades that looked identical, but the forged one (if made correctly) would be the better finished product.
BTW, I've been a machinist for 33 years. I've worked with many types of steel most of my adult life.