Difference between Garage and Collection

I’d like to understand the differences between the Collection view and the Garage view. I’m assuming that if you have multiple copies of the same car in the Garage only one will appear on the Collection but I wonder what happens if I get rid of all copies of a car in the Garage. Will it still count for the Collection? Or do I need to keep at least one copy of every car in my Garage to be able to complete the Collection?

I’m asking this because I’d love to be able to sell or gift the cars I’m not interested in driving but on the other hand, I’d also love to complete the collection. Any thoughts?