Originally Posted by Dan Burkhart

I've custom cut spokes for many entire wheels using my Hozan threader, and used it to complete the set for builds when I was a few short of the proper length. It is very labour intensive though, and getting spokes consistent in length is a challenge. Not to mention a set of rolling dies only lasts a few wheel sets worth. (When replacing dies on the Hozan, always ensure you get the ones for SS spokes.)
A pro quality spoke threader has been on my wish list for a long time, so after much consideration, and comparing options, I went for the Morizumi. Like I said before, I test ran a spoke with about half the threading cut off, and it seems to have picked up the original threads perfectly.
In this demo video by Ric Hjertberg, he cuts 274mm spokes to 269mm, which would mean he has at least 4mm of thread left, although he makes no mention of that fact. He just makes it sound routine.