The First Justicar

When my eyes first opened, the first thing I saw was a corpse. I didn't recognize it, but Severian told me it was 'mine'. I could remember Severian, and the others, but not myself.
Severian assured me that most types of transformation, both natural and unnatural, lead to amnesia. A butterfly can never recall what it was like to be a caterpillar. He told me that we'd been 'moved' into the armor, so we would be indestructible- incorruptible by bloodlust. Invisible to beasts that smell blood. He told me that the transition left my old body empty and dead.
But as my corpse was dumped out the garbage chute, I could see very clearly that the throat had been cut with a blade.
Why would he lie about that?