I don't know if anyone has come up with new science lately, but devine wisdom is "you can't re-heat treat spring steel that has already been heat treated". Most spring re-archers know that the re-arch won't hold, so they install an ignorant add-a-leaf into the package to help hold the arch. Problem with the add-a-leaf is it rides like hell. If someone has come up with a better re-arch that I don't know about- - -goodie goodie, I'm all ears.
You are correct. I have seen re-arch and be flat within a year. New is the way to go.