Being an assembly machine designer, a machine to assemble a knife would cost a few hundred thousand dollars: I think almost all knives are had assembled.
I'm thinking that to reduce cost, the tolerances on the grind for the liner lock, backspacers, etc. were loosened up and the extra washers are used to match the correct distance between the scales. No problem with it, just a work around to a preventing cost wherever possible. Benchmade has done this on a few of their nicer knives by using blade stop pins that were shorter in distance than the gap between the scales. The result is a smooth action because the pivot screw is determining the gab distance between the scales instead of trying to match the distance determined by the blade stop pin.
2 bronze washers should actually cause a smoother action, if the washers slide against eachother.