Hi Bud: An old timer that taught me to string back in 1968 taught me that knot,(never called it by any name), and said that no one else in our area used that knot back then. He told me that it would distinguish my work from others, I figured that since he was getting on in years at that time, and was parting with one of his machines(he was selling me his old Serrano), he wanted me to know this knot, as he was most likely getting out of stringing at that time.
From this , its evident that the knot was around for some time, and I figured that Parnell was probably the one who brought it to the rest of the well known stringers, and since its exact origin would be difficult to be found, that the knot was named after him.