Just to be clear, @gnoli’s current $OnAdd probably looks something like
Meaning that, like @wajakob, he is using the prototype mechanism to copy all the relevant metadata. (But unlike @wajakob, he removes the prototype designation after he is done using the prototype, so the list of prototypes doesn’t grow unmanageable.) If he no longer uses prototype assignment to do this, his $OnAdd will have to look like
$SourceTitle=$Name(parent) $SourceAuthor=$Author(parent) $SourceYear=$Year(parent) ...