The 000 for full door panels is based on what happens with B and A bodies....if you look at one of them, they have a padded insert on the door, and the lower and upper door is painted a finish color. The E bodies have a full door panel that covers the entire inside door area, so no need to apply a finish paint (000). A B or A body will have a paint code in that spot on the fender tag.
:beer: