User role referencing when they might not exist
Lets say there is a module in drupal which just does what you are asking for, how would you like it? :P

I found this module recently. TextNodeReference 

What this module does is


It creates a new widget for the references. Once the widget is enabled,
If the referencing node exists then it will store a reference to that node in the table.
If the node doesn't exist already on the system, then it will store it as text. But when the node with the same title is created, it will auto-reference it to the node.


Caveat : When that node doesn't exist, make sure that you are entering that right title(for the author or venue), and then use the same title when creating the actual node for that entry(author or venue).

You can thank me later, but do thank Boobaa who wrote this module.