Hollypossum,
I got the same talk from my vet when my horse was gelded. To me proud cut means there is some piece of testosterone producing tissue left in the body. It can be the small gland located on the spermatic cord or a person who gelds their own crypt and doesn't bother with the other testicles since it cannot be seen. When working around Houston as a teenager, I was shocked at the number of people who felt that hiring a vet to geld was a waste of money so they did it themselves. Lots of crypts who kept that internal testicle.