One more thing to consider. With its age it's probably had a few owners and somewhere along the line the buyer was told it was a Z71. Thus the subsequent buyers turned into sellers and the story stayed with it. If I was told is was a Z, unless that was important to me, I may not have questioned it. Good for you for asking guys that know.
yeah, that was my thought. He probably bought a "z71"
and never checked it, because unless you know what to look for, why would you?