A big thing that's leading to confusion is legacy information that can't easily be flagged as superseded. For a while, all D1s were referred to as Zerbe dies if there was a diagonal line by the U in UNUM or a dot by the first 1. This turned out to be incorrect, as many dies had that dot and/or a line by the U in UNUM. The problem is, that's a hard bell to unring. There are coins in
TPG holders that say Zerbe on them that have nothing to do with the dies used to strike his made-to-order coins.
The Chapman proofs are D1 reverses. I remember a VAMWorld thread that mentioned a D2 reverse die for a proof, but it may have been a later business strike using the Chapman proof obverse die. I can't remember exactly what it was.