Hey @Rob,
Thanks for reaching out—interesting question!
The way it works is that the importer looks for the matching venues and organizers by name first, then matches the IDs of the found venues and organizers and updates post meta in the Event post so that the items are linked together.
Adding columns and other customizations to the importer is technically possible, but is a rather complicated code customization to make. It is only possible with custom code. We cannot help with custom coding, unfortunately, but it is technically possible if you were to write the code yourself or hire someone to do it for you.
I hope this information helps!
– George