Early G3 G19 vs Late G3 G17, all same parts and vastly different trigger feels - why?

Ok, so I've been on a search for the cleanest breaking 4.5lb trigger with normal take up and no overtravel. I'm not quite there yet but getting close*. Issue I'm having is, I have two guns, and ALL the same parts in one delivers a clean break pretty much no matter what, the other is sometimes clean and sometimes mush depending on the combo. When I mean all parts - I'm talking about the housing, connector, trigger bar, trigger spring, striker assembly. How can this be?

- When I have the...

Early G3 G19 vs Late G3 G17, all same parts and vastly different trigger feels - why?