If you add a new property to an existing type it does not mean that all instances of that type will be affected. 

What will happen is that when you try to create a new instance then you will see the new property editor but all old instances will just have null/default(T) as the value.

Our internal type scanner always runs during initialization and tries to match code-based content type definitions with database.

Thanks Bartosz, that makes a lot of sense. 

I'm always just trying to pair my Opti knowledge with how things work in plain old MVC. Adding the detail about your type scanners work is very valuable!