If I could clarify:
The Chinese alloy that has been labeled 440A is not exactly 440A, but its performance is similar to that of 440A. Same for the alloy that has been labeled 420HC. It is not exactly the same as the 420HC alloy that Buck uses in Idaho, but its performance is similar.
This is a problem that Benchmade and Spyderco also had. When Spyderco first started doing work with a Chinese supplier, the supplier told Spyderco that the alloy in question was 440C. Spyderco did an analysis on the alloy and found that it was not quite the same, though the performance was similar.
My company has done work with companies in China. We find that, if we specify a certain alloy or material and the Chinese have something they consider equivalent, they use their "equivalent material" without telling us.
So this issue of "exactly what alloy is this in this Chinese product?" is not peculiar to Buck. A switch to the name "400 series alloy" may merely be indicative of a more accurate nomenclature rather than an actual change in alloy by the Chinese.