The introduction of MIM parts, as well as some manufacturing improvements of other parts (such as the drawbar), gave the newer production 3rd gen guns gradually improving triggers.
Besides some improved manufacturing, many newer production parts also benefited from being made to closer tolerances.
This is why if I ever have the opportunity to pick up a used 6906 (because I put a few tens of thousands of rounds through issued 6906's
), I'd prefer it to be a late production version, incorporating some of the manufacturing and materials improvements. The ones I used were made during the first couple years of 3rd gen production, and they worked well, but someday I'd like to have a late production one.