It's basically a "repsawn" per a cycle. So while you lost your chance by axing them off in chapter 5, you still have chapter 6 to try again. I'd suggest just soft resetting in the event you axe off a boss without stealing what you want.
IIRC, it's mainly Victoria, Victor, Kikyou (for the Brave Suit, though you get 3 without stealing if you've been opening up as many chests as possible and do the bonus dungeon), and Anazel that have the stuff worthwhile stealing, but it's been a couple of months since I last played.
PSN: Neophoton | NA 3DS: 2277-6964-8962 | JP 3DS: 2509-0978-4639 Currently playing: The Last of Us, Muramasa Rebirth