Not a set I've ever gotten into, but doesn't surprise me in the least. Most boxing releases, modern-ish or otherwise, have not really been known for their quality control.
The 1991 Kayo's are supposed to be seeded with autographed cards in the packs. I've opened dozens of boxes and I've never pulled one or heard of anybody pulling one.
If somebody did pull one, I'm not even sure what would differentiate them from the 1000's of base cards that have been signed at Canastota, at other shows and various events and through the mail since then.
I'm sure some exist and somebody could show me one, but they would be like chasing Willie Wonka's Golden Ticket to pull one from a box.