Sure there's corruption. Someone might convert someone outside of Lottery or Volunteer protocol for selfish reasons. It's risky though. Unless the Animal is killed outside of a Processing Centre there's a good chance the Butcher will notice when an Animal claims they didn't volunteer legally.

That being said. Once your an Animal, letting you leave could also spur on more people trying to say they weren't volunteered so, even if it's illegal, Processing will happen but an investigation is launched.

That said. Don't worry about being 100% accurate. The Lore Bible is just a guide, not a set of rules.