"My experience with Duco is that it "fuses " to the plastic nock. Look close and you will see where the Duco actually melted the plastic around the thin edge. With these nocks the plastic looks as slick and untouched as when before you glued it."
That's what I was going to tell ya to check. Duco works by actually melting plastic then letting it harden again as the chemicals evaporate out of it. When I glue on say a green nock and the little ring of glue is forced out of the nock, if I wipe it off with a finger I get green color because some of the green plastic melted out with the glue. If a nock is impervious to Duco, it may still be a great nock, you just might have to use another glue. Probably super glue would work well but most likely not over bare wood. Super glue would work better on a painted or clear coated surface. I wouldn't knock the nock just because it don't work with duco. It may be a really tough nock.