Having such a mix finishes on military firearms is not at all unusual. As you probably know, original 03A3s had a mix of blue and parkerized parts from day one. Late in the war, many K98ks had such a mix as did VIS 35 Radom pistols. My late war Sauer built LSR sniper also has blued screws in the butt plate. Looks great to my eyes, especially considering that is correct and original.