Without seeing the actual trigger parts, I can only guess, but one thing for certain is that "National Match" has nothing to do with any springs, especially single vs two-stage trigger pull.
Some target triggers are made from modified GI parts. The hammer spring is lightened, and much of the hammer is cut away to remove mass. But there still has to be enough energy in the hammer spring to reliably fire any kind of primer. A slightly lighter trigger spring can be used, too.
The trigger, which operates on the see-saw principle, has setscrews in the front and rear. The front setscrew determines how much overtravel the trigger will experience once the sear has released the hammer. The rear setscrew determines how much take-up the trigger will have before it engages the hammer notch.
These types of triggers can be adjusted, and mis-adjusted by the user. I had one, and after reading all the warnings about possible dire consequences, opted not to use them. Instead, I went with the newer unitized drop-in triggers. They operate on the same principle, but with optimized parts geometry, and everything is sealed to prevent tinkering. NRA safety rules allow a minimum of three pound trigger pulls. For a rifle that may also be used in zombie defense, I find that five-pound no creep, no takeup, no overtravel triggers work just fine. Five pounds feels like nothing if everything else is tuned properly.
My last two builds involved getting GI trigger parts to work better. Everything is factory stock, but working in the contact surfaces with Nanolube has produced (from the one that is now fully broken-in) three pounds of smooth takeup of the first stage, and another two pounds of crisp, clean-breaking pressure to actually fire the weapon. I specifically explain that to anyone who fires them, especially if they are used to GI M16-type trigger pulls. These triggers are not unsafe, but you have to know what to expect, otherwise that first round can get away from you.
Bottom line: single vs double stage depends on parts geometry, or setscrews, not "special springs". I do not trust my adjustments to remain fixed over lots of firing, so I've gone to commercial unitized triggers for all my single-stage trigger work. And careful tuning can turn GI parts into vey nice, crisp double-stage triggers, with a little work, a little care, and a lot of knowledge. My goal is always safety first, then reliability, and finally a "nice" trigger pull.
I hope that helps. Thanks for asking.