So as I understand:
items beginning quality is modified by crafters skill and a random number to get next item in production line.
As an example. If starting item is steel stocks quality 150 and crafters skill is lowest, then his crafted alpha blade will be quality from 100-125, beta blade from 75-100, delta 50-70. Or if crafter is highskilled, alpha will be 150-175, beta 175-200, delta 200-225.
Variables are just ilustrative, I am absolutely not sure if that is true, just what it looks like to me.